Colonization
You announced the current... dilemma to your crew, and quickly set about with your plans. First, you double the guard, making every single patrol and guard post on the perimeter about 20 armed men each, enough to deal with a decently sized attack. You also keep the APCs on standby with full troop loads. Some consider complaining, but the thought of what happened on the first was enough to make them reconsider. The survivors explained that the Aliens just used simple swarm tactics, running directly at them in huge groups, but they could learn, as shown by how, after the first few dead, the wounds stopped being on the chest and head, areas covered by standard issue armor, and started hitting the neck, specifically slipping in through gaps in the armor. The engineers and workers quickly get to work on the palisade, and, within a few days, it's less a palisade, and more a solid, concrete wall, covered with hidden turrets and firing spots. It would take no less then a horde to get over this wall, and you can rest more or less safely inside it. The farms are quickly set up, although they're just barely enough to keep the outpost fed, and aren't exactly pretty.
The scientists have some unhappy news. They studied seismic activity, looking for tunnels, and... they're everywhere. There's a catacomb of tunnels, all across the entire planet, all deliberately built. They seem to be designed for single file marching, and you appear to have actually landed in one of the only areas without any tunnels at all. They also found about 10 separate caverns, spread all over the planet, that could be alien-made. This is, of course, when the biologist from before runs over to tell you that the aliens look like they could have different castes, like ants, and if so, the workers could probably tunnel.
Meanwhile, the engineering and R&D team set to making mines make the Hopper. She's a beauty, based off of the ancient Bouncing Betty, but designed so the shrapnel flies much faster to pierce armor or chitin, and mass producible. They also made sure it was loud, too, so it could act like an early warning system in an emergency. It's one drawback is that it relies almost entirely on shrapnel for damage, and that something with much heavier armor could probably take one on the chin without even flinching. Finally, the last team of engineers comes back with their verdict on jetpacks. They had EVA suits equipped with short, burst jetpacks for repairs, but those were for space travel, where you don't need fuel to keep in the air. They say they would need an incredibly dense fuel source to make a jetpack that can stay up for longer then a minute, given their current technology.
Alien Activity
Things were mostly quiet for a day or two, then the raids started. Small, lightning raids, usually at night, but not always. The aliens usually lost these, getting out gunned by the patrols and retreating, but not always. Once, during construction, they rushed the site, attacking workers and engineers. They killed about 20 workers, but were quickly driven out by the guards, losing 5 of their own. One of the workers was never found. All of the blood stains in the site were tested, and any body parts left, but none of it belonged to him. Other workers swear they saw two aliens jump him, but, at least according to the evidence, he just ceased to exist.
Shortly after the wall was finished, a sergeant on patrol with thermal goggles saw about a hundred aliens sitting in the forest, just watching the wall. A few of them fidgeted towards it, as if something compelled them towards it, but none left the cover of the trees. He quietly sent up an alarm, but the aliens never did anything, just sat there.
People:
2995 Soldiers:
970 Workers:
500 Engineers:
500 Scientists:
Equipment:
3000 Rifles
20 APCs (Big, and armored. Carry 15 men each.)
2 Scouting Helicopters
Static Defense Set (Includes thermal-sensitive turrets, walls, and sandbags.)
Basic Construction Equipment (Few tools, fewer vehicles. Could probably build a house if given a week.)
The Arc (Basic Manufacturing Capabilities, Cramped Housing for all, and Small Lab.)
Makeshift Palisade. (Could be taken down quite easily by the Aliens, but it can hold them for a short time.)