Its just in my part of the world, using a GPS to mark a fishing spot is very common.  (My paddling partner does it all of the time.)  Spending time searching for bottom structure or submerged brush piles where you might want to return is an investment of your time.  The good news is, you find it once ... mark the spot with a GPS waypoint ... you can get back to the same spot next week (or even next year).  The two lakes nearest my home are about 29,000 acres.  This means that you have lots of places to search and some length of water to cover.

Of course, you could just re-invest the effort that went into finding the spot the first time ... but why?

dd