Nogales, AZ is the border tunnel capital of North America – at least for tunnels US law enforcement knows about – with 53 having been discovered so far. Subtopia tells us about them in the first of a multi-part series. Their primary point is that DHS, by building the border fence, has literally forced the smuggling underground.
It’s the “show me a ten foot fence and I’ll show you an eleven foot ladder” neologism making an even bigger nuisance of the fence’s impotence here via the tunnel
The migrants move both ways while drugs go north and weapons move south. Enormous drainage tunnels that link both countries make things considerably easier for them.