I built this a few months ago,,just recently redid it it by removing the old pond liner which was a vapour barrier,and digging it 3 feet deep in the center. I replaced the liner with a real pond liner (which I saved up for !!) and now it's done,,,I plan on building a cover for the winter out of fencing and vapour barrier sheeting,,to keep heat inside as much as possible.
as well as running a pump..I have 2 koi and 7 gold fish..