Get an air horn. When I lived in dog country I got one at a boating place designed for small boats, it weighs less than a can of pepper spray, and then made a mount for it on the handle bar. It puts out 110 db. This will bring the dog to its knees a good fifty feet away - dogs have sensitive ears. My experience is that this is a much better alternative to sprays - stops the dog further away, doesn't harm the dog, you don't have the risk of it blowing back at you or crashing while you try to aim the spray.