i know you would enjoy watching the ducks swim around in your pond, or even a swan. BUT, once ducks take up residence at a pond they multiply. And multiply again. And again. Then besides feeding on your fish and pulling up flowers, they poop. They poop in your pond and on your grass and on your paths. A dozen ducks can foul a 20,000 gallon pond and literaly cover your garden with duck poop. My vote would be to DISCOURAGE any ducks from taking up residence at your wonderful garden.
Of course, if you are determined, borrow some decoys....Just be careful what you wish for...