I have a new technique idea. Mow them down with machine guns and drop napalm on them. Do it at random times and places, but frequently enough to keep at least a 10% fatality rate per attempted border crossing. I think that would be an excellent deterrent. You wouldn't even have to police the entire border. Just brutally massacre and incinerate them 10% of the time. As the vast majority stop making attempts, you could concentrate and incinerate 100% of the illegals. That would do it. Very efficient.