How about our very own military doing the shooting and protecting out borders. You don't shoot them on the outside of the border, you kill them on the OUR side of the border. Clearly posted sighs in many languages... will shoot to kill any trespassers.
Rather simple. You come illegally, get shot in the attempt...tough.
Even IRAN doesn't kill its trespassers.
U.S. hikers jailed in Iran may be released after bail is paid - CNN.com