How much water are you holding back ? What fish do you have in the pond ? You could be sitting on a dangerous situation. If it were mine, I would probably try 1) Give up 50% of the water and try a heavy layer of betonite. If that doesn't work, and you're less than 2 acres, try ML's approach and pack the backside with clay. 3) Maintain steady doses of betonite every couple of weeks and try to wait it out. 4) Dump clay from the front 5) drain and get the dozer back in to put a 2' clay layer back down.
It's not the end of the world, I have seen dams that leak more than yours, 50+ years old and leaking since day one.
