My first option would be to energize the military’s active denial systems, discussed in earlier threads, as soon as the invaders get within 50 meters of the border. That keeps most of our men out of harm’s way with respect to rocks and bottles. Systems can be aboard hovering helicopters or drones on our edge of the border, giving rapid relocation options.
Live ammo can and should be used against ANYbody who breeches the buffer zone and steps foot on our soil.
A note can be attached to the toe tag on the carcass that says ‘Sorry ‘bout that, Chief” in as many languages as necessary. This IS war, after all.
Why not take 1,000 ft north of the border and give it to Canada tomorrow? Then the migrants would be entering Canada not the USA. Quickly build a fenced camp. The migrants would think they are on US soil. Let them get settled and then inform them different.