One my of my ponds in built on mostly rock. Deepest point is 12 ft average is 4.5-5. Pond was built well over 30 years. Been chasing a leak for several years finally identified an area that is around 20ft by 20ft where water seems to find an opening down through the rock and just runs straight into the ground. I dug it out with my backhoe this summer and packed a lot of bentonite and even concrete but seems like it continues to find a way down through the rock. My backhoe isn’t large enough to pull some of the larger rocks out that are buried several feet deep. Largest one was around 8 ft across and estimated at several 1000 pounds. Thinking about getting a triaxle load of good clay and just covering the area and pack it really well. What would you give my odds at that working ?

I'd contact teehjaeh57 here on the forum and ask him about the polymer sealer that he has. It would be way less expensive than the clay. Shoot him a PM and see what he has to say.

I've tried a polymer before it doesn't work on large holes. In this particular area I can go 2 months and then I'll have a hole the size of a softball show up all of a sudden and I'll lose 2 inches in a day until it goes below the hole.

Then clay and a sheepsfoot roller are about your only options.