I have a male boxer (1 year and 3 months old) who we were planning on breeding so he is not neutered. Our apartment complex has a dog park which I brought him to last summer and he was very submissive and got along great with other dogs. We did not go much over the winter, and now that I've brought him back again he is extremely aggressive towards all other dogs. It doesn't matter if they are male or female. I read up on it a bit and tried introducing him to other dogs while on his leash, and tried to distract him when he seemed to be getting upset. Nothing is working. I am thinking of getting him neutered as to stop this aggression. He has also started marking things in the house, so that is another thing I am wanting to stop. Any advice or help??