I was told that you could never stop a leak over a sandy soil area for your pond. I have added clay and will core the side next to the dam. It might not stop the leak, but shouldn't it slow it down some. It leaks down about 1/4 to 1/2 inch a day. When it reaches a certain level it stops and the small area behind the dam dries up. Any suggestion!!!! This has been happening for about three years.