I have to disipline biting with my ducks since they live inside and get picked up often.... My method of disipline i got form Nancy townsend, who was the first person to keep ducks/geese indoors. In her book, "Duck, there's a goose in the house", she says you can disipline them. Here's how to do it....
You have to start the disiplining while they are babies in order for it to stick with adult ducks. I don't disiplin normal nibbling or "tasting". I only disiplin them when they do that big "stirke" move and the other duck yelps or moves away. (So, in other words only hard bites or bites that are causing harm to another duck/goose). I point at the offending duck and say no loudly and firmly. That usually distracts them from their biting. You'll have to do this over and over and over again... You will NOT see results right away. You can also tap the beak with your finger (not hard) and say "No BITING!" again in the firm voice. I also use my index finger and thumb to hold the beak closed (lightly, if the duck struggles, don't hold it down, it could hurt itself) again with a firm voice saying no biting.
If you are still having problems after a day or two of non stop biting, you can also pick up the goose and hold it lightly around the neck (not restricting blood/air, just loose enough to make the goose look you in the face without wiggling away. I make my finger/thumb into a ring right under their chins. then they can't get away or move their head out and they don't get hurt). Make the goose look at you in the eye, and without laughing lol (that's the hard part), tell the goose again "NO BITING!"
You'll have to do this many many many times, without results... Then sometime in the future, you'll just notice that they stopped biting. It takes about a week with my ducks. If you keep up on it they should stop. MAke sure also spend some time holding them nicely and talking sweetly to them so they don't get scared of you. Don't disipline them if they are just nibbling on your finger or each other. That's a normal behavior. Just disiplin those big strikes. I had to majorly disipline my little duckie vinnie two days ago when he bit my neck really hard. Little bugger almost drew blood. I did the holding of the neck thing and told him no biting.
I used this method with my two oldest duckd and niether one bites people/each other/ or even the baby ducks who bite them! They are very good about it now. Hopefully this'll help!
Note: If you are uncomfortable holding the goose's neck/holding its beak/tapping/etc then don't do it. You don't want to hurt your babies.