I've read for years that turtles do no harm so I haven't bothered with them. Fortunately I have seen no snappers.
However....after planting an expensive water lily which will not spread to deed water something curious happened. It grew great and bloomed with 7 or 8 pads. Then we found the pads floating to the bank. After inspection it was obvious that something had chewed through the stalks. The first thing that came to mind was a turtle. What else could it have been? I can't afford to have $25 lillies eaten.