A wall on a border? That's ridiculous. Everyone knows they're racist, they're isolationist, they're too expensive, and they ultimately do nothing but show your own intolerance of other lands and peoples. That's if you're the United States, of course. For the rest of the word, walls seem to work pretty well.
Tunisia has placed a barriers, walls, watchtowers, and moats along roughly 50% of its border with Libya. Considering the mess next door, and recent terror attacks, they're understandably concerned about keeping the threat at bay. Surveillance is expensive though. So, of course, American taxpayers will be footing at least part of the bill.