I should have said earlier....3 minutes! OOPS!
Hurting you or someone else is a big issue. If you can NOT do it yourself, get a professional who deals with bull headed issues. It'll cost you some money, but it is better than getting hurt. Like I said, you have to be firm and if you can't do that out of fear (it happens to the best of us sometimes), get someone who isn't scared of that particular issue.
Reading your last comment makes me think it is an attention/boss issue. I've had a few that were spoiled by their owners and had to sensitize them back to who is in control.