“what about tunneling?”
The best solution for tunneling is sensors, rather than more concrete.
It is not feasible to put thick concrete down 60 - 100 feet, and even if you did, without sensors to detect tunnels/tunneling activity, they could tunnel through that concrete as well as the soil.
Modern sensors can detect a lot - they can even distinguish a human footfall from a deer, as well as digging activity quite deep down. They are also much less expensive than burying more concrete.
The best solution is a wall and a fence (double barrier), with some exclusion area wired with sensors - at least buried vibration sensors, but they could also have lights and cameras in urban areas or around gates.
Another approach to countering tunnels, is to periodically patrol with ground penetrating radars, which can be towed behind vehicles driving along the length of the wall.
https://en.wikipedia.org/wiki/Israeli_West_Bank_barrier
They use a 200 ft exclusion zone where possible.
Without an exclusion zone, multiple swarms can overwhelm the system.
Probably not much of a tactical gain, but a strategic gain; massively increasing US manpower requirements.
Yes. I have been told technology can easily detect tunneling in the areas where there is no dense population, which is most of the border.
Tunnels are nearly always in the cities, it is easier to disguise them with the network of underground storm drains, utilities, things like that make it harder for technology to sort out what is normal.
We all have to remember, no barrier can stand alone and do the job. We have to have technology, regular patrols. We must have the barrier, an absolute message that THIS is the border, and we do not want illegal crossers. That sounds like common sense but what we have now for miles is old barb wire livestock fence and illegal aliens and smugglers have claimed they “didn’t know” they had crossed the border. We have had the Mexican military cross the border and make that claim. The barrier has to leave no doubt it is the border, then we have to defend that barrier.