This may be a possible cheaper solution for you. I had a leaky dam on my 1.3 acre since it was built 4 years go. My pond never stayed more than about 1/3 full.
I ran into a friend at the feed store who recommended somebody local who might help. This man builds, ponds, roads, etc. He came out and looked things over. He said that he thought my water was likely all going out through the dam and not the dam and the bottom. Since my pond had water and was stocked I didn't really want to drain it which he had suggested. He told me he had repaired leaky dams before by building up clay from the back side and that it could work in my case since he thought my dam was on the thin side (15' at the base). Since I had material readily available on the back side of the dam, he started pushing it up and compacting it in 6" layers. The pond is nearly full (well past where it leaked before) and no leaks; holding fine. There are no guarantees this will work in the long haul, but he is pretty confident the problem is fixed. My fingers are crossed.
After getting bids in the $18,000 - $26,000 range to repair the leak, this $1,200 fix is a blessing. There are two large ponds across the street from me that have large dams with no cores built in and they hold water fine. The only difference they have from mine is that the width of their dams, from the base up, are much wider than mine.
