I did have a pond liner in the past, but the concern was the pool. And last year our winter was messed up and I lost all my fish and don't want to take that chance again.I was just curious. Sometimes people do it out of a concern that their fish will suffer in the cold. Others just enjoy watching their fish all winter.
So if you've done it successfully in the past, why are you questioning whether you can do it again? Is it the type of container you're using that you're wondering about?