Make absolutely sure you can outrun the dog. A medium sized dog I had easily outrun 3 or 4 times before, apparently saw me coming and jumped out of some bushes directly in front of me. I hit him and finished my ride in a ambulance. I was in the hospital 3 weeks with broken ribs, collapsed lung, etc.

Hitting a dog can be a far bigger danger than getting bit. Getting off the bike and keeping it between you and the dog is the best option, in my opinion.