Hey billert; good to have ya postin'!
I have to be the bad cop on this one. I don't want you to get your hopes up and start makin' plans. I recall a thread within the last year or so about this same thing, and I thought the idea got fairly well trashed.
Personally, if I was digging a pond small enough that I could afford the experiment, then I would just do the right thing and put in a correct liner. If I was digging a pond large enough that I couldn't afford a bad decision, I would dismiss vapor barrier as a liner and use conventional methods.
BTW, all this comes from Mr unconventional risk taker, willing to spend $100 to save 50. Also, stay clear of Theo's possum innards until Sunil samples one of his possum innard sticks.