I had my SandShark in the sea for the first time yesterday. I have tried the Tiger and HH Wader on the same beach two months ago and found nothing. This time I had a bunch of coins in the area where gravel meets sand. In that place, both VLF detectors were useless and now I know why - the small gravel is sticking to the magnets in my scoop. I would bet any waterproof PI would work there, I just happen to have a SS and it works great.