I think if he is drawing blood, that is more than enough. When he gets too wound up, it's time for a break. I would stop them, and put him in his crate. Mine play very rough, and they are all bullies, but sometimes they get "over wound up", and then I say that's enough, and quit. Bentley needs to learn to quit when you tell him, and give Coco a break. Like kids, they just don't know when to quit.