John:
Based on what you said about your friend and gunnite, I'd definately go for the gunnite...
This site:
http://www.pondpetsusa.com/newpond.htm will show you how Tom's pond was built from the time he cut his first grass sod out until the gunnite was completed... Somewhere else on this board is the completed project...do a search for Tom, and it may come up or if Tom sees this he may post a path to the site...
He sealed it with CIM... If money is no object, I'd look at polyurea spray...again check out Mike Ms thread on the polyruea pond project in this section... Depending on your soil conditions, you may be able to spray the polyurea directly onto the soil which is covered with a thin membrane...KOI USA has an article about a pond built this way...( Two to three months ago)
Hope this helps...
Aloha! Mike