Esopus, in looking at the Deer Stopper website (see thread on 'great deer spray product') I noticed there is a new product called "Goose Stopper". Don't know a thing about it, but you might want to look into it.

Here is a link that might be useful: Goose Stopper

Dogs...

If there was an easy answer here the golf course guys or the airprt biz would have found it years ago. Whizbangs (fireworks from a pistol) have been somewhat effective if regularly applied, but the annoyance to the waterfowl is likely to be less than the annoyance of neighbors, especially if they're close...

Tryu planting an area with duck potato or another favored food (may keep them there instead of your garden areas; like putting out corn for the squirrels)

Try the dogs; there are airports using them to clear runways...

What about a fake raptor? They use real ones to scare pigeons away from airports. Might work with ducks.

At local golf courses, they use black pepper as a goose repellant. Purchase in large quantities at a warehouse-style grocery store.

i know for geese (and it probably works for ducks too) the best repellent is to plant a buffer of tall grasses and wildflowers around the pond so its not easy for them to walk in and out of the pond. they will of course fly in on occaision, but they wont make a habit of hanging around a long time if its difficult for them to walk in and out. this is why golf courses and urban lakes have such a problem with geese populations the short lawn grass is typically mowed right up the edge of the water.

Try a taste aversion. GooseChase is a biodegradable food-grade liquid repellent is sprayed on grass, making it unpalatable and inedible to ducks and geese. They leave for better, untreated food sources.
Besides that you are going to use an organic repellent that is not going to damage your plants. One gallon of product per acre. Reapply every 7-14 days or after mowing.
GooseChase repellent is most effective geese control when used synergistically as part of an integrated bird control program combining visual scare devices.
I hope you try Bird-X product and hear back from you on how the product solve your duck problems.
You can reach Bird-X at 1 800 662 5021

Here is a link that might be useful: Bird-X GooseChase duck and geese repellent