Leaky,
I hope you get the contractor to fix the problem.
I have not followed all the links but somewhere someone should have mentioned the obivious:
After the pond leaks down, you will know exactly where to apply the least amount of mud / lime / glue / mattresses / dead bodies / water turkey carcasses / turtles beavers.
This would be the least costly as you should be able to repack the area once it drains and dries out a little. On the bright optimistic side.... After it drains, you may be able to fix the problem with a shove or an hour of backhoe work.
If the pond dams blows out before it leaks down, rejoice, at least you will have a true target to hit.
Good luck.
