You buy the big one,,usually called a Bear Stopper, you have to buy 2 and practice with one,,even letting a little blow back in your face so you know what it is like. Pepper spray is usually allowed in almost every state, some states have a limit on precentage contenet, which is actually meaningless but you have to make sure what ever it says on the can complies with state laws.

Contrary to what you read in the papers, pit bulls are the number 2 friendliest dog breed(next to the Golden Retriever) when it comes to people. They are extremely dog aggressive (agrressive towards other dogs). So if you stop face the dog, he will most likely come and lick you lol. I have one pit bull that doesnt like bikes..but would never harm the rider. Never turn your back on a dog that is coming for you.

I ride almost every day, when a dog comes after me, I dont ride as fast as I can, I slow down and the dog usually will run on the side of me till I get away from his territory, I stay calm and usually have no problem.