Why not end our foreign aid to Mexico? In fact, why not end ALL foreign aid and kick the UN out while we're at it.
I like all that, PLUS the copious use of M2 .50-cal MGs and Claymore mines that others have already mentioned. For my contribution, I'll suggest exploding collars, such as they had in the movie The Running Man, for all illegal scumbag aliens that are caught and deported. That way, if they try to come back in, the problem is automatically solved at the border.
Scouts Out! Cavalry Ho!