I don't have any advice on how to stop it, but I know how you feel. My boxer is the same way. She will be as friendly as can be with ANY female, but if a male comes around, other than my husband or my father, she just goes nuts barking, and her hair stands up on her back. After a few minutes of them being around and she sees they don't pose a threat, she'll calm down, but if they make any sudden moves she's back in her "charge" stance. She has never bitten anyone, and she has never been abused, as we have been her only owners, but I have no clue on how to make it stop...