Yes, I had a big, strong, powerful handsome black male who was a dream to train. He started showing aggression about nine months old toward other dogs, no matter the age or sex. As he got older and more sure of himself, he got worse. He snapped at my eight year old niece, hated cats, and looked to pick fights. His thyroid was tested, he had no other health issues. I consulted a very good trainer and worked with him for five or more years. He just kept getting worse. At nine and a half I made the agonizing decision to put him down. My nerves were in shreds. He, and I are at peace now.