I inherited an ancient Whites metal detector from my grandfather when I was small. It must have been made just after transistors became cheap (this thing is ooold). By modern standards it is probably not much more than a toy (it was a high end model when it was made), but my brother and I found all kinds of stuff with that thing. We lived on the coast so plenty to find on the beach; but the coolest stuff came from the ~250 year graveyards. Old old belt buckles, buttons, handles (I guess from the coffins

); we didn't give it much thought at the time but probably shouldn't have taken that stuff. Also lots of old forts and battle grounds from various wars (South Eastern U.S. coast), so more buckles and buttons and bullets and such.
It finally broke down and I've been meaning to get another ever since, it's a ton of fun finding stuff. That one should be waterproof (the coil that is), so you can fish around in the water at the edge of the lake, banks of rivers, people lose stuff all the time. Go for it!