Duck want a shallow area that they can turn upside down and filter through the mud with their beaks. This is why they flood the fields here in North Alabama in the Winter for the Ducks that over-winter at the Wildlife Refuge. I would dig the pond with a 12 - 18 inch deep shelf around the perimeter from the edge out about 10 - 15 feet and then do your rapid drop-off from there for the fish area. Just my suggestion from what I have seen of the Ducks in this area. Bet Bob Lusk has some good info on this. Bob