We have a beautiful almost 12-week old that is exhibiting VERY aggressive behavior, especially when he is told "no" or stopped from something he wants to do. He literally is showing attack behavior and it is scary. We are holding him down until he gives up and then leave the room for five minutes until he calms down. So, two questions: WHAT is happening -This is not normal behavior for a berner right? And, what recommendations do any of you have for behavior modification? Thanks!!