I am in 7a (perhaps 7b now) and I would worry that two feet deep is not deep enough or perhaps large enough either. I also question your basic assumption that preformed is easier or more convenient than a liner. I agree that one could hang a preformed unit in some kind of frame; perhaps in a deck; but even that takes a bunch of framing or hole cutting and then one would have an uninsulated pond bottom that would almost certainly freeze solid. To get good insulation requires digging a hole almost the shape of the preform which is a pain.

I think it is far easier to dig a hole without specific concern for its shape and heave some liner in it. Well, actually, grab some old rug out of a carpet company dumpster and throw it in first. Then you have an insulated pond. Just dig one part deeper than two feet.

I have several 300 gallon Rubbermaid stock tanks that are sunk into the ground. they are about 24" deep. You just need to make sure the plug is in good. I've had mine about 15 years.

Catharinet, what zone are you? Is that a steel tank or plastic? How big are your fish?

Chaos, thank you for the thoughts! I guess I'll read about pond liners before I decide. Long ago I had a preformed pond and I don't remember the installation being difficult...but that one was smaller. I worry about ripping a liner, and the hard ones last basically forever. I remember standing in it, I probably dropped things in it.... I guess maybe I could make it double thickness.

She is in zone 5 (see after the name). And yes, it is easier to dig a round flat hole than an odd shape. But back to liner, regular liner is very thick and doesn't tear except under extreme circumstances. That certainly makes it harder to move around than a tarp BY FAR (costs way more too), but especially if you don't worry too much about wrinkles by covering with rocks, plants or logs etc. it is far easier to install. Like I said, heave it in (well, drag it in).

Hi Ann.......sorry I was gone for awhile. I'm in central Indiana. These are poly Rubbermaid stocktanks. What kind of fish are you going to have? I don't have fish. I decided they were too much work. So I just tend to have lilies, marginals, frogs, tadpoles and sometimes snakes. If you have lots of wildlife, you probably should prepare yourself for your fish getting eaten, especially if you have a shelf on your little pond. Straight down sides are best to keep out animals like coons. I live out in the country. One day I came home and there was a great blue heron sitting on top of the house, checking the pond out. :o But I think coons are the biggest threat to your fish....or even stray cats.