We used to do a bunch of work for a pool company ans the designer swore on this stuff called "zypek".
Basically its exactly the same process Bill S. wrote about said except this stuff actually expands when mixed with water.
Its some kind of high tech epoxy based polymer.
There's a big supply house out here called "WhiteCap" and they carry tons of high end stuff for your fountain.
A liner wouldn't even be necessary.
One other thing, I've seen the plumbers out here use roofing firms to actually 'hot mop' their fountains. I'd look into that, if you get a leak you'd have somebody to fall back on. But the technology in hot mopping been around awhile, don't think you'd get a leak for years, then do the Schwab thing and 'smear some more'!
http://www.primeresins.com/products.php