I tried the same thing the other day with a big golden retriever who came out onto the road towards me barking angrily. I stopped and used my most deep loud voice and shouted "No! GO HOME!!!" and pointed away. He stopped right away, hung his head in shame and ran off home. I was amazed. This may not work with german shepards or dobermans, but I think it has a good chance with goldens and labs, etc.
I keep pepper spray at hand's reach on my frame with a bungee.
If i was ganged up on by nasty dogs like you describe, I would stop my bike and spray them. They would probably never chase my bike again. If their owners won't teach them I guess somebody else has to. You could be seriously hurt.