Neutering doesn't fix aggression even though that is commonly believed and recommended.
I suggest reading this paper,
Aggression toward Familiar People, Strangers, and Conspecifics in Gonadectomized and Intact Dogs and recommend referring people who suggest that as a solution for aggression to read it. There are reasons to neuter, but aggression is not one of them.
From the paper:
I would recommend contacting a certified behaviorist, there are publications that cover the issue and recommended solutions.
I can give some references if you like, but agression is not a simple fix; it requires a solid understanding of behavior modification and rigorous methods or it can become dangerous and should not be attempted without a thorough understanding.