[RummyChick]

How are they going to deal with tunneling under it?

[Pollster1]

How are they going to deal with tunneling under it?

Tunneling is much slower than running across open land. My suggestion is not meant to be perfect, just to slow the criminals down. However, if the double fences are far enough apart, and if the border is monitored to see where people are still crossing, we should be able to find and destroy the tunnels as they build them. Throw in one more barrier well beyond the double barriers of concertina wire, and it'll be expensive to build a tunnel that long.

[mrmeyer]

Flood them or demo them once discovered.
http://www.popularmechanics.com/military/a2487/4244235/