We recommend breeds that are designed more like wild ducks, as they tend to have a slight advantage over several "man made" domestic breeds. Heavy meat breed ducks tend to be slow, cumbersome, and unable to fly. Hence could be easy pickings for predators. As Amiga stated, snapping turtles can be a concern for all waterfowl. We've had large snapping turtles rip a mature Canada Goose gander's leg to shreds, before he could exit the pond and they can kill ducks. What predators are in your area?
Ducks that are pretty self sufficient are: Mallards, Black East Indies (BEI) , Muscovies and pet quality call ducks. These breeds can fly, which is advantage if predators are a concern and are excellent foragers. They usually stay close to pond, if there is sufficient food stuffs. They also tend to be excellent mothers, hatching and raising their own broods. BEI are beautiful in their striking black feathers with a shimmering green-purple sheen. Muscovies and call ducks come in a variety of colors and patterns.
Geese are grazers, so they prefer the pasture around the pond. They will bathe and play in the pond and it can provide some safety. African and Brown Chinese geese can make good "pond geese". They aren't so heavy that they are slow, like the larger heavy goose breeds. They may be able to fly/flap short distances and are good foragers. Many can hatch and raise their own goslings. Plus, these breeds are beautiful and often referred to as having a regal look.
Hope this helps. Good luck.