I would like to endorse a product that works for me: HALT!
I have been chased more times than I care to remember while out running or cycling...about 8 months ago I purchased a product called HALT!. I have carried the small clip-on bottle with me ever since. I have not had cause to actually use the stuff until yesterday and today. I was out riding yesterday when a group of dogs ran through the open fence of their yard and gave chase. I immediately began pedaling faster and shouting at the lead dog, but "he" continued the pursuit. I deployed the pepper spray...small bursts aimed at the lead dog...the spray didn't actually hit the dog, but I believe the smell was strong enough to discourage the pursuit.
Today, same house, different dog came through the open fence and chased me a good distance...again, I deployed the pepper spray and was able to discourage the attack. 15 minutes later in the ride, different house, different dog came out of the yard with the look of harm in his eyes and sounding like he meant business. I managed to spray this dog right in the face and he immediately dropped to the ground and began rolling around, discontinuing his chase. Lastly, I had two dogs chase me for a considerable distance, right before the end of my ride... I was concerned they were going to collide with my bicycle and cause a crash, so...I let loose a small burst near the lead dog and they swiftly discontinued their chase!
These dogs were doing what dogs do...acting like dogs...it is the owners who should be punished for allowing them roam freely...However, I should not have to suffer an injury due to their owner's lack of responsibility. So...I have chosen to use a non-lethal method of deterrent that I can happily report works exceptionally well!!!
HALT! Get yourself a container and clip it to your belt while you run or ride. Works great against aggressive animals, and if necessary against aggressive humans!!