Much of what was previously posted about aggression in chickens applies to geese, but there are a few differences I want to talk about.
Ganders instinctively guard their family, with the intent of raising young. A rooster’s caring often stops after the mating, though some show their hens where a good laying spot is, and some will guard and even care for chicks. With geese, the family oriented behaviors are the norm, not exceptional at all.
Geese are smarter and have better memories than chickens. They may be the smartest of all the commonly kept poultry. This has advantages and disadvantages. They remember encounters with you, and seem to consider how to change your behavior as you are trying to change theirs. Maintaining eye contact with an aggressive gander is the first step. If you ever act afraid, they will not forget that episode and work to repeat it. But there is no reason to be afraid, even the largest gander is not capable of inflicting actual harm beyond bruising your skin and ego. So, when you enter the space with an aggressive goose, march straight towards him, keeping eye contact and forcing him to decide whether he can stand his ground or if you are maybe going to catch him. In my experience, they always turn and run away if you move toward them quickly and decisively.
Now that you’ve established that you are bigger and faster, and not the least bit afraid of him, the gander will always be on the lookout for you and issue a warning to the others whenever you appear. He may still look for an opportunity to bite you in the hopes of eliciting a fear response, so always be aware of his location, otherwise you might get “goosed”.
If your gander was tamed as a gosling and knows you well, his familiarity with you may make him more emboldened. My young ganders would nibble on my fingers as goslings, but as adults, their nibbling is no longer sweet, but motivated by hostility. It makes them harder to deal with as they will come right up to me with little fear. They want to dominate me and make me run from them. I never run or act afraid, in fact I lower myself to be less of a threat and use goose fighting techniques to establish dominance. I treat this as a game and try to play if frequently. In the game, I am going to pat the goose on top of their head. This is how dominant ganders bring others into submission, but putting their head over the others and establishing that he is bigger and taller. So that is what I do with the game I call “Pat You on the Head”. They hate this game because they are always too slow to win, and soon move away and acknowledge my dominance to the other geese.