Bob's right. The plastic liners available at Home Depot are generally used by painters to lie under their work area. The cost is less than 25% of what you might pay for Firestone Pond Gard. It comes in 6 and 8 ml and various lengths and widths. I've thought about using it to line a pond and then cover with soil to improve water chemistry and prevent UV from breaking down the liner. It's certainly worth consideration. Durability and UV resistance vs. cost would be the determining factor.
