They are steadily building a solid wood fence completely around the back yard. It's pretty unusual that you see such a fence in this neighborhood. Usually you see dividing fences and chain link.

(We had a 100' long fence built as a buffer for one neighbor that doesn't enclose the property.)

I'm wondering if literally they are creating a compound to fight being deported/detained. They already seem quite paranoid about any contact with neighbors.

Yeah, I'm paranoid. I haven't seen anything like this before. It doesn't feel organic and natural. Usually third world people aren't anal about boundaries, they let their toy dog run out in the street. I think they are planning to fight or go to siege mode.