I think, with the advent of drone warfare, tunnels and the like are going to become more and more relevant. Maybe we'll see one of these in the near future:
I wonder if tunnels can be detected with ground penetrating radar (GPR). They are already planning on using drones to detect mines.
This sounds like a good idea if they could swarm the front lines with these drones and be able to drop charges on each of the mines. Even if it can just detect the ones large enough to blow a hole in an AFV.