You want 'challenging' ? Try using a LRL & rods on the water and underwater. We don't have any choice as all the 'finds' we've made since 1980 are in the ocean on wrecks.I had one in the early 1980's, tried using it in the Arizona desert, wind blew it in everywhere. One day I took it apart, it had a bunch of wires and resistors to form a circuit that did absolutely nothing. I put it in the closet, years later ebay came into existence, I sold it in the early 2000's..
make some dowsing rods, they are cheaper and will do more.