15-17 mil Thick isn't thick enough? it notes they've been used as pond liners..(and i'd love to have a white liner to see in the ft!) i know that the firestone pond liner is 45 mil thick..
i might give it a try, i'm thinking of using railroad ties instead of masonry blocks.. could probably build a 300+ gallon pond for under $100, this would probably be made in my basement, so wouldn't have to stand up to the elements so to speak