I've just starting carrying a product called "Direct Stop Animal Deterrent Spray" that I got at Mounds Pet Food Warehouse. It's billed as a safe and humane way to deter aggressive animals. It also states that it may not stop all animals. It's a citronella based product. This will be the first product of this type I will have tried. I usually either ride away from a chasing dog or stop and talk to the dog.