If I can't out run a dog or I judge him to be possible threat I usually get off the bike and do one of two things. Put the bike between myslef and the dog, try to find a large rock or pine cone and throw it over there head. Most will go after it, beacause we all play with our dogs by throwing something for them to chase after. But have another object to throw as a back up. Another option that has worked for me is pick up a large hand full of pea gravel from the side of the road and hurl it at the dogs feet. It will confuse them and the noise of it hitting the road sends them scurrying. It may not work for all encounters but it has not failed me yet.