I know that border. I lived along it and I ran it more than a few times. So long as this is Xanadu no walls or towers are going to keep any one out.
Those valleys have been a passageway to the north since men hunted mammoth in the valleys with spears and rocks. The ancient porchteca, Aztec merchant princes, regularly traveled up the San Pedro to the Gila and across to California. For three hundred years Apaches and Commanches used it to raid deep into Mexico, until raiding trails were beated into smooth wide roads. Geronimo and Juh crossed at will despite the best efforts of Crook's patrols. The Clantons, and other border riffraff, used those trails to bring stolen cattle up from ranchs below the border.
420 miles of wall, manned 24 hours a day might slow but won't stop the immigrant surge. Those willing to risk the Camino del Muerte won't be stopped by a wall. If anyone starts shooting women and children on my border I would be back down there in a heartbeat. It isn't going to happen.
We have chosen to have a welfare state and this is one of the costs. We have few choices but the best are to (1) End the welfare state and (2) Have a robust guest worker policy. They will still come but at least we can make order out of the chaos and have some controls.