The Wall.

Can't be done. It'll remain a patchwork of fence and wall, patrol and drone. Big Bend Nat'l Park cannot be walled (you're seriously going to try to put a wall in the middle of deep treacherous canyons, and if not cede lands to Mexico?). Neither can Lake Amistad.

As I've mentioned before, Emperor Qin (China) was smart. He used stone faced rammed/piled earth for his 'Great Wall'. Most components were in-situ. And raw components are the issue here. Along with the design (walls have never been effective deterrents - they have ends).