Bullies do play rough, but when they get too rough, you need to step in and stop it, like you have been. Maybe even break it up as soon as you think they are getting a little too rough. He is only 1 1/2 years old and still has a lot of pup in him. He will not settle down until he gets over 4 years old. Neutering him will not really help, in fact for the first few months after, he may even get worse, as his hormones will be going crazy. Just stay on them and stop the play when it gets rough.