Grainger - $20 - Lifting and Retrieving Magnet, 2 in Overall Length, 2 in Overall Width, 100 lb Max. Pull - Item #9UDF7, Mfr. Model #07541...
This should pull most anything that goes plop in the pond. I have one similar and have retrieved dock hardware, glasses, my trap, and it's great for collecting nails/screws after a day of barn demo...very handy. Harbor Freight has some cheaper ones, but I'd visit a store to make sure it's power is good enough.
