I like the idea of a border fence but one guy with some bolt or wire cutters could do massive damage. I am not even talking illegals here, some of our very own OBL's might be down there letting more in.
(A) The proposed border fence is not your typical backyard home fence that you chat with the neighbors over; it is made out of thin but durable wrought iron, which is criss-crossed to prevent climbing over and will be electrified
(B) Border patrol units would patrol on the other side 24/7
(C) There's no need to build a huge, Great-Wall-of-China like wall when a fence can do the same job at more than two-thirds off the cost
I'm sure we have the technology to prevent this.