Fishy, are you talking about tagging the bullfrogs or turtles? I think it would be neat to tag a turtle, see if it stays or comes back. I'm afraid one tried (and probably succeeded) in burrowing down into my bog a year ago, causing the tear that caused a leak in my koi pond bog last spring. I don't necessarily want them in there, but they are welcome to stay if they can do it with no damage to my liner. Otherwise, I assume they leave and find mud somewhere to burrow into, then are drawn back to the water. I have the farm pond, too, so not sure why they come to my koi pond instead! I love it, though. Always fun to have them come on their own accord to visit my ponds. Bullfrogs I'm finding out stay, or at least some of them do. I had probably 8-10 large ones last year. I know they would eat baby fish, it's just trying to figure out how they could possible catch them once they are about 1" long that I cannot fathom. They are not fast swimmers, and the little tykes can surely out maneuver them. No worries here, though, I let nature take it's course. Don't need 100 baby koi swimming around my pond every summer. I know the fish eat the majority of the eggs and fry, too, so why not let the turtles and frogs have a few. LOL