Matrix Morpheus

Then how do they keep prisoners in?

Walls cells and guards

Walls and guards would keep a majority out. Cells wouldn't be needed.

They would tunnel under. Theve already had tunnels under the border

Well nothing is going to prevent some from trying, but the numbers would be very low. Tunnels take a lot of time to dig and then when they are found *boom* all that work lost. Walls would prevent a whole lot of illegal immigration...but,not 100%

Yes. Walls fencing properly used with patrols. But only would considerably slow them down. And make them take the ocean route.

Then we give more money to Baywatch for the extra patrols. I like the way your thinking. :)