so, how is this going to work? what are they going to do?

i'd expect a kind of swiss cheese of border upgrades. they'll build a very small amount of wall in a very strategic location to allow for a photo op. and, trump will certainly keep telling you that he's building a wall, and then claim he succeeded in it, too.

kind of like "mission accomplished" in iraq....

then, ten years later, they'll do public opinion polling and 40%+ of people will think he built a wall.