Chen Hao grabbed a handful of mortar and rubbed it in his hands; his skin felt a little itchy. Just as he was about to stand up, Nana's optical glasses suddenly turned north, and the alarm beeped once.

"Seven large life signals detected." Her voice remained unchanged. "They are 3.2 kilometers away and their speed is increasing."

Chen Hao's hand trembled, spilling plaster all over the floor. He looked up at her: "What did you say? A wolf or a bear?"

"The specific species have not yet been identified, but they are all more than twice the size of standard livestock." Nana was already walking towards the sled. "I suggest we return to the base immediately and prioritize protecting the sheepfold and crop areas."

Chen Hao slid off the rock with a thud, his legs feeling a little weak. "Wait... we've only just dug out some ore, how come even wild animals are joining in the fun?" he said, pulling out a walkie-talkie and stuffing it into his pocket before staggering back.

The night wind stung their faces. When the two rushed back to the base, it was still dark, and the sensor lights along the edge of the farmland were flashing incessantly. Nana pulled up the thermal imaging screen; several red dots were moving down the gentle slope of the valley, the foremost one already approaching the eastern fence.

“They’re after the food.” Nana scanned the area around the sheepfold. “The smell of leftover feed from last night has spread too far.”

"So what do we do now? Shake them away with gongs and drums?" Chen Hao asked, panting as he leaned against the wall of the tool shed.

"The temporary solution is feasible." Nana activated the broadcast system, playing a noise mixture of metallic clanging and low-frequency booming. A few seconds later, the red dot on the thermal imager paused briefly and then began to slowly recede.

"Effective?" Chen Hao's eyes widened.

“For now,” Nana said, turning her voice down. “They’ll adapt. Next time they might need a stronger stimulus.”

“Then let’s build a wall.” Chen Hao slapped his thigh. “We still have some aluminum alloy plates left. Let’s weld a barbed fence around it. We can’t let them roam around freely.”

Nana paused for two seconds: "The material is enough to cover the main area, but it needs to be welded manually. Your strength hasn't recovered yet, and there's a risk in doing it."

"I'm fine." Chen Hao waved his hand. "I can't sleep anyway if I lie down, so moving my hands will warm me up a bit."

As dawn broke, the two began their work. Aluminum alloy sheets were removed from the old equipment rack, cut into strips, sharpened at one end, and then fixed to the ground with supports. Chen Hao squatted down to weld, sparks flying everywhere. When his hands were burned, he would shake them off and continue working.

"The progress on the east side is 60% complete." Nana stood beside her recording the data. "Note that the vines on the right side are quite dry, so be careful not to ignite them during welding."

"Okay." Chen Hao replied without looking up.

As soon as he finished speaking, a soft "snap" was heard, and a string of sparks jumped into the pile of withered vines next to him. The flames shot up and were only half a meter away from the crop area.

Nana immediately pulled out the liquid nozzle from the robotic arm and sprayed the residual liquid from the biogas digester over it, extinguishing the fire instantly.

Chen Hao wiped the ash from his face: "I almost burned my house down."

“The probability of an accident has been factored into the subsequent process optimization.” After Nana finished speaking, she opened her backpack and took out a square device. “The sonic beast repeller has completed its initial debugging. The frequency can be adjusted from 1,000 to 20,000 kHz.”

"Then why don't you give it a try? Pick one that can scare away wild beasts without startling sheep."

Nana mounted the device on the fence post, set it to 18kHz, and pressed the start button.

At first, it was quiet. Five seconds later, the goats in the pen suddenly raised their heads, ears perked up, and then began to frantically ram the fence. Two strong goats knocked over the newly welded joint, and a piece of aluminum alloy plate fell down, smashing several seedlings at the edge of the flower pot area.

"Hey! We're guarding the outside, not the inside!" Chen Hao rushed over and grabbed a sheep that was running around wildly.

“The frequency exceeds the range that goats can tolerate.” Nana quickly turned off the device. “The database shows that its sensitive frequency band is 14 to 16 kHz, and the current setting is at the peak of the stress response.”

"So you mean we did something good but ended up doing something bad?" Chen Hao sat down, panting. "This thing is worse than an alarm clock."

“It can be resolved after adjustment.” Nana reprogrammed, “The new target frequency is set to 14.5 kHz to avoid the peak response of farmed animals.”

"Alright then." Chen Hao rubbed his arm. "Anyway, half of the fence has collapsed now. Let's fix it first."

Before noon, they reinforced the collapsed section and installed sonic booms at three key points. During this test, the sheep merely looked up and showed no unusual reaction.

But the alarm sounded again at night.

"Three signals are approaching from the west," Nana warned.

The sound wave was activated, and the red dot stopped ten meters away from the fence, lingered for a while, and then retreated back into the valley.

"Looks like it worked." Chen Hao breathed a sigh of relief and sat on the toolbox, munching on some dry rations.

“Defense efficiency has improved, but long-term effectiveness cannot be guaranteed.” Nana stared at the data stream. “Some individuals are showing tentative forward behavior, which may indicate that they have learning capabilities.”

"You mean they'll become bolder?"

"The logic holds true."

"Then let's add something tougher." Chen Hao finished his last bite and stood up. "I remember there's a thorny vine over there at the mine. It grows fast and hurts when it pricks you. Let's plant a ring of it around the outside and see who dares to climb it."

“Thorn vines can have root systems that can reach a depth of 1.8 meters, making them difficult to climb.” Nana pulled up the plant records. “The recommended planting spacing is 0.6 meters to form a continuous barrier.”

"This is it."

The next morning, they brought in a batch of vine seedlings and planted them in trenches dug outside the fence. Chen Hao was responsible for supporting the seedlings and filling in the soil, while Nana used a robotic arm to compact the roots. A sonic transducer was embedded inside a metal column, linked to a vibration sensor. If any living organism touched the surrounding vegetation, the system would automatically trigger an alarm.

By evening, the defense line was largely complete. The inner layer was a spiked metal mesh, and the outer layer was newly grown thorny vines, interspersed with three sound wave emission points. The main control module was connected to all sensors, monitoring the surrounding area in real time.

“The overall structure is stable.” Nana checked the last pillar. “The dual-layer defense system is now in standby mode.”

Chen Hao walked around the entire area and found that there were sparse vines in the southeast corner, so he replanted a few. He tamped down the soil with his feet, and as he straightened up, he suddenly noticed several fresh scratches on the bottom of the western fence.

"Wait a minute." He crouched down to look. "This mark... looks like it was gnawed with teeth?"

Nana scanned the metal surface and said, "There are subtle bite marks on the metal surface, strong enough to cause slight deformation. It is speculated that the attacker had a strong bite force and the intention to climb."

"So, ordinary spikes might not be enough to stop it?"

"We need to strengthen the protection of critical nodes."

“Then bury the bottom edge deeper and add another ring of sensor wire.” Chen Hao stroked his chin. “If it dares to get close, immediately sound the alarm. We’ll prepare in advance.”

“It’s feasible.” Nana pulled up the wiring diagram. “The vibration sensor wire can be connected to the main controller to trigger the instant response mechanism.”

The two immediately got to work. Chen Hao dug trenches and laid cables, while Nana welded and reinforced the base. Before sunset, the entire defense line completed its final upgrade.

In the darkest hour before dawn, the alarm sounded for the third time.

"Single target, located on the west side." Nana's voice rose half an octave.

Thermal imaging revealed a larger red dot than before, slowly approaching the fence. It stopped outside the thorny vines, sniffed for a moment, and then suddenly lunged at the metal mesh.

With a loud bang, the entire section of the fence shook.

Chen Hao rushed out of the guardhouse and saw the shadow scratching at the bottom with its front paws, trying to crawl in. He could see clearly—it was nearly 1.5 meters tall at the shoulder, with long whiskers hanging down its mouth, and its eyes glowed yellow in the night.

"This isn't a wolf, it's a mutant..."

Nana simultaneously activated her sound waves, spreading out high-frequency sound waves. The creature paused for a moment, took a few steps back, but didn't flee. Instead, it let out a low growl and rammed into the fence again.

The stress alarm lights up in red on the control panel.

"The local structural pressure has reached the critical value," Nana said.

Chen Hao stared at its footprints, growing increasingly alarmed. "This guy... isn't afraid of thorns or noise; it really intends to force its way in."

"It is recommended to reinforce the western node immediately."

"It's too late." Chen Hao grabbed an iron rod. "I'll go see where its weakness is."

"The risk level is too high; human approach is not recommended."

"Do you have a better idea?"

Nana didn't say anything.

Chen Hao gripped the iron bar tightly and slowly approached the fence. The beast turned its head and stared at him, letting out a low growl.

Just as it lunged again, Chen Hao slammed his fist on the metal pillar, creating a loud bang. The beast froze, its movements slowing for half a second.

Nana seized the opportunity, activating the ground induction wires, causing a brief release of current. The creature twitched its front paws and jumped back two steps.

"It works?" Chen Hao turned around.

“Low voltage pulses can cause discomfort and should not be used continuously.”

"That's enough," Chen Hao said, panting. "At least we know it's afraid of electricity."

As dawn broke, the wild beasts finally retreated.

The entire defensive line trembled, but it remained unbroken. Chen Hao drew a circle at the southeast corner of the fence, marking the location where thorns needed to be replanted. His clothes were covered in mud and resin, and the burning itching on his arms was still there.

Nana stood to the side, her optical mirrors continuously scanning the horizon. The high-temperature deformation of the robotic arm's outer layer had not yet been repaired, but she continued to run the monitoring program.

Sunlight climbed up the metal spikes and shone on the silent sonic boom.

Chen Hao bent down to pick up a fallen vine and was about to throw it into the recycling bin when he suddenly heard a muffled thud in the distance.

He looked up.

At the edge of the forest that had just been driven back, the ground trembled slightly.