IF you cannot get away and aren't armed...wrestling works a lot better against dogs than boxing and kickboxing. It will certainly get ahold of a limb, but try not to panic and definitely don't play tug of war with your own arm. Instead..invite it closer, shove whatever is in its mouth more in its mouth, wrap your other available limbs around it's respiratory/circulatory bits, and choke the life out of it. The first two things violate a dog's instincts. You're giving it more of the arm, and not trying to escape. Then factor in that all things considered, we have more attack options than a dog. You just have to somehow maintain composure, accept you're gonna get hurt, and that you have more attacking options than the dog if you drop your humanity for a second and go caveman.