What I've described is what I would do "in a nutshell" of course there are many details that I didn't go into and deatils to work out, but I think it's possible, VERY possible.
Build a BIG ass fence - think berlin type of ("wall") fence (barbed wire, big trenches, open spaces in which can easily be seen by either gaurd tower, etc.), and have every few hundred feet manned by a real human being.
From Brownsville Texas to San Diego Calf.?
This strikes me as
1 silly
2 futile
3 Not gonna happen.
No flame intended. Just saying my say.