The vinegar/water is probably a good idea. I just use water from my bottle - so far, so good. A little Accelerade (or whatever you happen to have with you) in the eyes would probably make an impression, without doing any real harm. Stopping and letting them know you aren't taking any guff seems to work well - take away the incentive and the fun. And the dominant voice is key - "screaming "bad dog" at the top of my lungs", maybe not so much - just excites them.

It seems like the ones who really mean business sometimes don't bark - they like the element of surprise. Like the only one who ever bit me - he'd bark his head off every day when I walked by his house on my way to the ski trails - until that one day. He didn't bark because he knew he wasn't tied up that day! One minute he was standing silently by his house, and the next he was slipping up behind me to grab my calf. The ones who have really chased me on my bike have generally been very quiet. I had a Great Dane in my past who would race along in the field by the road, as hard as he could, until he'd get in front of me, and then just step into the road, to see if he could send me flying over him. Meanwhile, I was riding as hard as I could down the hill by his house, to try to stay ahead. I always had to hit the brakes.

I sure wish I knew how to handle my own chasing canine! She has never chased a bike (thanks to the invisible fence and the distance to the road), but she loves everybody, loves mountain biking with me, loves jumping on people, and has chased a couple of slow-moving cars (very scary). And she just stampedes our two cats (but I think they love it, actually). She is a long-nosed flying shepherd (50% Aussie & 50% German). I'm afraid to take her anywhere within 1/4 mile of a road, and she isn't so good on a leash before she gets a few miles in. I'm positive she'd chase a bike if she could, but for the fun of the race, not to bite anybody.