I have but offshore in the oilfields, due to your water depth and I assume no diving experience(also it's not the safest thing to do solo in water) you would be blind dredging if you were to put it on a pole or rope and lower the rig to where you want to excavate it would work. But then if your pond is clay lined you run the risk of punching through your clay.

Here is an old thread where I explained the process. If you need any more assistance feel free to hit me up and I will get back to you as soon as I can.

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Main=32990&Number=431921#Post431738