Reading this article reminded me that in years past I have sometimes
had a bit of luck by sticking a hose in a tunnel at a high point and
letting the water run strong for an hour or so. Makes for an
interesting irrigation, with water coming out of the ground at
disparate spots.
I have wondered if we could kill them if we were to rig up a hose from
an exhaust pipe and push carbon monoxide into the tunnel system. Might
just cause the engine to stop, from the resistance.