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Not seeing you are online, so I will proceed with your consultation.
At 3 years of age, Buster's "maleness" is very well engrained. Thus, while having him neutered is a good first step in trying to cure him of his aggression, it is not a guarantee that it will relieve him of it. While the testosterone will dissipate from his system over time, its effect on his demeanor may be so set that it may not make a difference. Time will tell.
Regarding time, it can take as long as 3 months to see an improvement in hormonally induced aggression. Thus, if Buster was neutered only a month ago, there is still hope that things may get better.
If ultimately the neuter procedure does not help to quell some of Buster's dominance aggression, I would advise high level counselling for him, from a highly trained canine behaviorist. There is a company called Barkbusters that has a central training facility in Denver, that trains all of their therapists with a consistent an uniform approach. There are therapists all over the country that have the same training. My Barkbusters therapist has been pivotal in helping many difficult behavior cases among many of our patients with issues. She has made me a big believer in their training approach. You can find a local Barkbusters rep at:
Another option, or perhaps an option to consider in conjunction with behavioral therapy, is to consider putting Buster on a tricyclic antidepressant. Prozac sold generically is commonly prescribed for canine behavioral cases. It is inexpensive, often very effective, and safe. My own yellow Lab is on Prozac for severe separation and thunderstorm anxieties. I have also been success full in treating dominance and overprotective aggression as well.
Medications like Prozac work by causing a net increase of the neurotransmitter, serotonin, in the brain. Serotonin is the neurotransmitter associated with feelings of joy and contentment, while suppressing feelings of fear, anxiety, and rage.
Best wishes to you and Buster. I am going to exit the chat now, but you may feel free to follow up with me in question and answer mode if you wish.