Don't hit it on the head. Their heads are like tanks. I'll you'll do is make them mad. The lower neck will stun them good.
True, you can't swing a fully loaded bike, but still good advice if you aren't loaded. Bottom line, take advantage of what you have.
Spray is worthless. He did a demonstration where he had his dog attack someone (in protective gear) as the person tried to spray the dog with fake pepper spray. Even knowing the dog was coming the guy couldn't hit the dog. You're more likely to hit your riding partner.