Tell me walls like they had at 'Helm's Deep' wouldn't make the Border Patrol's job on the borders easier. Note the doors along the ramparts that swing open that would give the Border Patrol a clear shot at any climbers with their new pepper ball launchers, while still protecting them from projectiles.
There's the guys that can build them for us. Peter Jackson's crew look like bonafied experts at building those fortificationss.
Look at all the room for advertising space on those walls!
Can't you just see the McDonald's, Pepsi, Coke, Kentucky Fried Chicken and Sears industrial, digging, drilling and cutting tools ads on those walls, now?
Those walls would generate a positive cash flow! ;^)