“All the guards in the world are not going to keep out people who want in.”
Plenty of land mines, a couple of bombing ranges, and a shoot on sight policy would do wonders to keep the illegals out.
But that is still going about it back asswards.
Hit the employers such that it doesn't make sense to hire illegal labor, because right now it doesn't make economic sense to NOT hire illegal labor if your competitor is keeping his prices lower by doing so.
As soon as the jobs are not made available, they will leave and not try to come back.