man i have heard every rumor there is about ponds, hogs, clay, toilet paper, and 4 wheelers, but the one thing that has always worked is check with your county extension agent, the hogs also seem too work pretty good, they will make a mudhole that is for sure
BTW, i have a good friend that put his pond where he wanted it, and the county ext. agent told him "yea that would be pretty, but it'll never hold water", and boy was he right, in the wet part of the year it is beautiful, but most of the year it is a big deep hole with water running thru one section of it (from underground[:@]) so my suggestion, call your county extension agent, hopefully he can save your pond
good luck, i have felt your fustration before