This may sound crazy, but, toss the dog a couple of dog cookies. Even dangerous dogs can be trained if the trainer knows how to handle it. Dogs chase things that run, period. It's what they do. If you feel like investing the time if you stop and get off you're bike with the bike as a shield, you may start gettiing the dog to expect a treat every time if you do it consistently. You could eventually become more important to the dog than his owner calling him. I trained a dog that bit me to wait for me to stop and give him a treat and a pat on the head. It requires learning on the part of the rider, but it works. Get a 4 dvd set of the dog whisperer and watch all three dvd's as if it was homework. Experiment with safe dogs first. It can be done.