One reason I mentioned before for rebuilding this pond was the fact that it clearly had a serious leak somewhere. We were adding water every week, which we had never done in past years. Then, once we tore out the old liner, we found the leaks...animals had chewed holes in the liner in a few spots. Our pond is surrounded by our wooden deck, which is just inches off the ground in most places. Consequently, it's an inviting place for rodents, like rabbits, squirrels, chipmunks, etc. Plus there are weasels, raccoons, and moles all over the place. So I decided to but some welded-wire "hardware cloth" screen in rolls. I plan to put it down CAREFULLY beneath the underlayment, with about 2 inches of soil between the metal wires and the fabric underlayment. I HOPE this will keep critters safely away from the liner, WITHOUT becoming a source for wire-punched holes on its own accord. This will add a layer of complexity to the project, but we found small tunnels during our digging, and don't want more holes chewed in the new liner.