my cement pond would crack about every other year. I did the sealing caulk method and the re-surface method. It would still get cracks. I got smart and bought a heavy-duty pond liner. It is a flat flexible rubber like sheat with a lifetime warrenty. They come in muliple sizes (small to BIG BIG) from Trickers water garden in Independence, Ohio (near Cleveland) It was some good money up front but have never had a leak since. When you consider the money and time spent repairing cracks the investment was well worth it. You can find them on line.