I've got a Fenn MkIV trap but I'm not having much success in coaxing
the little bleeders into its jaws. I've dug the trap into the earth so
that its treadle plate is pretty much level with the soil and then
covered the whole trap with bark chips to make it more or less
invisible. I bought a metal tunnel with the trap, and I've covered the
whole set up with this. But despite scattering a few peanuts around
and inside the tunnel I've had no luck. They eat the nuts outside and
carefully avoid the tunnel. I thought perhaps they didn't like the
strange metal tunnel, so I've tried a couple of house bricks with roof
tile on top - no success that way either.

I don't much like the idea of poison for the sake of the squirrels or
other wildlife, so plan B is an airgun, but obviously a trap would be
a lot less work (and less vulnerable to my appalling marksmanship).