Have just finished building a Surf PI. Only spent a couple hours on the beach so far, seems to work quite well found tent peg, nail, $2 coin and a bit of ali can. Goes off on basalt type rocks also. Mounted on a forearm crutch, housed in a piece of 50mm pipe with 3 li-ion batteries. Coil was wound from cheap hookup wire from jaycar on cardboard, housed in epoxy coated corrugated carboard. Got all my info from the Geotech site. Will try and post photos shortly.