I constructed my pond mid march this year. I used a 22mil pvc liner that claims to have a 15 year life. The stuff is very tough. I have stacked very large rock right on the thing in several spots, and my 80lbs pitbull has been in it numerous times. No holes from this summer, knock on wood. I bought two of the liners, and intend to add on. The hole is dug and prepped, and I'll be installing the liner tomorrow. If the seam seals, itll be just over 2500 gallons. My seams will be in channels of shallow water...i hope it holds.