I don't believe shooting at illegals is a solution to anything (assuming I'm not being attacked by one.) However, that said it certainly can be honestly posted on signs along the border - "Caution, enter at your own risk."
I do believe ranchers (and others) with property along the border are tired of being invaded. I really can't blame them.
I'm not advocating shooting anyone, I'm merely saying that you need to say that illegals are being shot at an alarming rate. It would at least slow down the timid ones.