I made a 10' search coil extension cable for my Bounty Hunter
Discovery 1100. I separated the electronics box from the detector and
put the box in a floating, waterproof plastic food container w/lid.
I can search water up to 5' (before inhaling water). Very little junk
in beach water at 2 feet to 5 feet depth-so you can use any cheap
detector and find good stuff!