I would warn of a couple of possible outcomes with using pepper spray.

One, if the owner catches you spraying his dog with spray it is highly likely that he could chase you down, run you off the road with his car, assault you, and get away with it. Ask me how I know this.

The other is that you catch any of this yourself and accidentally blind yourself, or other potential riders if you are in a group, and the outcome is likely to be much worse than being chased by a dog.