Put out ads for a few good snipers and post them (the ads) along the wall.
To help stop this invasion...
ICE could SELL .308/.223 rounds, at cost, laser engraved with registered numbers on the base of each slug to US citizens who want to stake out any section of the border...
Dig out the slug, and ID the marksman...He/She gets a monetary reward to be agreed upon...Preserve anonymity of the shooter...
There are countless shooters among us who could make a decent living doing this, and the FedGov would save money in the process...Leave the body to decompose as a warning to other Invaders...