Although this is politically impossible the most humane barrier is a mine field. Each year many hundreds of illegal aliens die in the deserts of the Southwest trying to gain illegal entry into our nation. Last year it was about 400 bodies found. The real number is much higher. Their bodies lay undiscovered in the deserts. Only the insane would try to cross a mine field. Thus these many hundreds of deaths would not happen in our deserts. The caravans of illegals would stop.
What is more humane, a mine field that would kill just a few insane people, or hundreds of deaths in the deserts due to thirst and heat? It is not a nice death. My numbers of deaths does not include that of the caravans and the rapes and indignities committed against the women in these caravans before they reach our border.
Rumors are there are mines that eject tiny flechettes that render a person unconscious...it also alerts authorities via satellite with the serial # of the mine so they know exactly where to collect the victims.
They can be deactivated by serial # via radio.
Hard to defeat, have pinhole cams to allow for only firing on adults while missing the head/eyes....cams work in the dark.
Main problem is if someone is rendered unconscious during the day and the sun winds up damaging the eyes....but generally the eyes close so you have some time to get to the site...or a small drone could swoop in and shield the eyes.
Israel is rumored to actually have neutron mines that CANNOT be tampered with, pop the tiny selectable-yeild warhead up a short distance and can wipe out an entire tank force and infantry force. The sensors are not located at the mine site but very near.
Mine tech has come a long way.
I am NOT a fan of mines, the old ones that could lay in wait for many years are especially evil.