If you want too see and read something fascinating, they make a bear spray for people who might confront grizzly bears and other strong predators you might run into, wild. http://www.udap.com/ Someone once told me that would really be way too strong for a dog. I think it's got a lot of the same ingredients as dog spray but to a much higher level.
They make a pepper mix to mix in with birdseed I believe that the birds can eat but squirrels can not eat it.
I'm sure, there is a way to make your own spray, spray from a bottle if real important with pepper or other additives that would deter a dog. It just seems it'd be a hassle to carry along a little plastic bottle, dish washing soap size or something but if it was a real problem, maybe. I see someone suggested a water pistol on the first page, sounds reasonable.
I read the air horn post, I think that would be a good solution and our store sells them. I haven't really had a problem with dogs, I heard the old fashioned silent dog whistles effect dogs as well.
This past summer, late at night, I was riding, keeping the story short, across the road, this fellow was walking a pit bull late at night, those kinds of dogs are close to illegal and I wondered, why would someone be walking the dog at 9:30/10 pm at night, maybe he shouldn't have one and though across the road, that thing noticed me and did take a bit of a minor turn at me and the owner pulled him up right away. I almost felt like reporting the darn thing to the police so if something like this was happened frequently, I'd definitely arm myself with something and an air horn sounds good. I felt really vulnerable in that situation.
It sounds odd, I've read a lot on this subject, if you don't have anything, use the bike as a weapon. I know some of you have expensive rides but not moi
by the way.