“You mean like these tunnels, below, that were built under the U.S./Mexican border under the currently existing portions of the Fence?”
As I remember, they used it for running DRUGS, not people. Try running a 1000 or so people through there every day and how they’ll avoid detection, on either side of the border.
Why build a tunnel when they can blow up the fence:
"After masked men blew a series of huge holes in the border fence late last night, thousands of Palestinians streamed through the holes and swarmed the streets of the Egyptian border town of Rafah, clearing local shops of whatever they could manage to buy and carry off: milk, powdered detergent and the occasional motorcycle."