Hi Everyone, My husband and I have an almost 12 month old Bernese Mountain Dog. He has been living with us since he was almost 4 months old. Since he was about 6 months old, we noticed that when he was tired, Cooper would become grumpy, just as everyone does when they are tired. This included behavior such as nipping at our hands and/or clothing as well as aggressive barking. We have noticed that he is becoming more aggressive, especially when he plays. Cooper LOVES to play, especially throwing a ball and/or playing tug of war with rope toys. However, he seems to rough house when playing, as if he doesn’t understand how rough that he is being. For example, I was throwing his favorite ball around with him and he was enjoying it. I threw it, he stopped, and he began to lash out aggressively (barking, nipping, growling, jumping up on me). I turned my back to remove myself from the situation and he continued to show aggression. My husband and I have tried to be stern, divert his behavior with toys, use calm tones of voice, etc. We do not know if we are doing something that upsets him, causing the random aggression? 90% of the time Cooper is very loving and always loves to be with us. When we attempt to discipline and teach him right from wrong is when we see the aggression. I understand that he is still a puppy and learning, but if we can change how we train him to help alter the behavior, that would be amazing. Thank you for your advice and thoughts!