If you are willing to fight another man, you should not be scared of a dog. A dog is no where near as dangerous as another man in combat. I have had to fight both, and I can tell you from experience a dog was far easier to defeat than another man with decent fighting skills.
Also, dogs can smell fear. The more fear you display, the more they will go into attack mode on you. You cease from being something big they may not like to something big that ignites their predator vs prey instincts. Show no fear, and 9 times out of 10 they will eventually back down. The last 10% you may have to exert your dominance through force though, so be ready for that possibility.
