Hi nightshade and thanks for the welcome!
The preformed pond is a bit of a long story - I took some taddies home from a friend's pond for the kids to watch in a tank...and then couldn't bear to part with them as they began to turn into froglets!
The preformed pond shell was given to me by someone who was fed up with it, and at the time, couldn't afford liner so...I dug that one in, thinking to make a more natural shaped one with a soft liner at a later date (which I did, in September this year!)
Kait