Walls are expensive and pointless. They go under and over them now.

The tunnels are usually dug from one building to another. Limiting their crossing to those areas makes it much much easier to track them than them sneaking across a wipe open space that we don't have enough manpower to monitor.

tunnels under a wall are much easier than drug tunnels

They have tunnels under Loredo and Brownville that are 50 years old and (I've heard) big enough to walk upright through.

Maybe they’ll build a wall over them. That’ll show them.

Thank for the upvotes sir