I fear getting females will do more harm than good. Geese are already aggressive animals, and when they are protecting mates and young, they bring it to a whole new level. You'd also need to get at least 4 females, though more may be needed depending on how the ganders treat the ladies. My other worry is that the females will be aggressive wanderers too, and now you have a little gang walking into the road and harassing people. My opinion? The boys are just fine without the girl, but you may feel differently.