Usually just find the smoothest spot on the rock he's on and pick at it on one edge if you don't have nails, Just kinda press and slide one finger over the same spot for a minute, or you can repeatedly touch the edge of his foot with a piece of ice, Just don't hold the ice on him, or you can take the rock and his ffot out of the water and coak the edge of his foot. Once they start to release in one spot you got em, as long as you don't cut the foot you are all good. They are really pretty tough critters, just don't use anything other than your finger or ice on them so you don't cut the foot.