Land mines, artillery practice, target practice, sniper training - all of this.
On the opposite side of my point that the best way to deal with illegals would be to target the business that hire them, I'd also like to point something out regarding how the situation will not be handled.
Anyone who is not familiar with the modern conventional military should realize that there is no way the U.S. Army is going to employ lethal force against unarmed men, women and children. It won't be ordered to, and even if it was, the orders wouldn't be obeyed at any level.
If that's your plan, then you don't have a plan.