I had a potpond for a year or three before I finally decided enough was enough and dug a very small real one. Just made it from a 16" plastic pot, with a pygmy waterlily in it. I had to put fish in to stop bugs eating the lily leaves, and wire mesh to stop herons helping themselves to the fish, but it worked very well. When I moved to the real pond, I tipped the contents in. One fish still going after 4 years!
It was horrible to clean out though. I am dreading having to do this to the main pond. Not this year... :)
moonbells