[Raellus]

I prefer a dry moat/berm wall over fencing. A chain-link fence is not much of a barrier. It's really not much more than symbolic. A station wagon could plow right through it; it wouldn't trouble a small team with wire cutters much either. Unless it was well covered by fire, it's not going to stop any but the lazy and least determined.

In general, human-power is going to be the primary means of excavating/earth moving in a T2K environment. If it means protection from existential threats, most local citizens would be willing to contribute to some sort of defense works project. This is really the basis of the neo-feudalism that I anticipate would be prevalent in a T2K world. You wouldn't even necessarily need motorized excavating equipment- just picks and shovels- I'm sure you've seen pics of Soviet babushkas digging AT ditches on the approaches to Moscow. A motorized excavator would be a luxury that many communities would not have. Those that did, however, would be able to complete defense works projects much more quickly efficiently. Such equipment could serve as a form of currency in a T2KU and securing said excavators could make a side quest for a community-building campaign.

Another option for creating walls/barricades is derelict motor vehicles. Tow or push them into position for a simple barrier. If one had to the means to stack them, you could create a more effective obstacle.

You might want to consider a hybrid with a little of every method mentioned so far. Chain link facing the marsh, a moat/berm along the most approachable part of the perimeter, wrecked cars for half-a-mile on another side, and a couple of shipping container redoubts with guard towers at intervals all along the perimeter.