About the only way to keep it from happening is to get 2 of the same sex preferably females. it's pairs you have problems with because the gander doing what ganders do best is very protective of his mate and goslings too if any are around. 2 ganders would work also but they will want to mate with the female ducks.OK, so I have been considering getting two geese to help protect my flock of chickens and a few docks from the occasional raptor. However if they are destined to become chicken and duck bullies I will definitely not want any geese. I'll must lurk in the background and see what other bits of info emerge.