I do wish you luck with your gander. In no offense, are you positive that he's a male? If he's not mating, he may wind up being a female. If not, you might be able to try keeping your geese in the future and simply getting another gander, seeing as he doesn't suit your needs.
After going on 6 years old I know hes a gander and I don't plan on getting rid of my big boy lol I know he mates my goose just not the new one hes not when i had 3 females he was getting aggressive towards me because all three were biting him to be mated when he mated one the other two would bite him etc