You mean, shoot them. Otherwise, deportation and physical barriers are already in place.
As the final means of stopping them, yes, shoot them.
As for the rest of your post.
Deportation. Deportation takes weeks. In the mean time they get free meals and shelter paid for by us. Solution. Gag and bind them like the GitMo detainees, bus them back to the border and drop 'em of on their side.
Physical Barriers. You're wrong, we have virtually no barriers outside of the entry and exit point that are guarded by the inept INS. Solution. Erect a wall. Digg a really deep trench. Staff the border with Marines. Whatever it takes to make it really hard to get across without getting caught.
EBUCK