How about carrying a kid's water pistol filled with vinegar and water? Probably easer to aim than a water bottle and covers a bigger distance. You could put it in your bike jersey pocket.

OK, kind of a silly idea, but I bet it would work .

I live in NYC where there are very few loose dogs, and I never untill this moment thought about the dog danger on my occasional rides in the country. Good thing to be aware of for the future.

Our big dog danger here is long easy release leashes - several bad accidents caused by the biker hitting a leash they didn't see. Not good for the dog either.