re: Concerning the Gaza tunnels:

Pipeline to pump water in from the mediterranean, use directional drilling technology from the oilfield to run it to the highest tunnels they can find. Let gravity do the rest, and flood them. Even if they start pumping them out, IDF should be able to see where water is suddenly flooding out of the ground. If you are someone who built access to the tunnels under a building, then well... actions have consequences.