Pepper spray.
If you go to sports and outdoors stores, you may notice there is both a "pepper spray" and a "pepper gel". Get the spray. The pepper gel is only if you are sure about your aim, are worried about backspray (getting it on yourself), good for human assailants. The spray is cone in front of you which is better for animals which move around a lot.
Forget only pitbulls, really. Any dog can be dangerous. Do not consider all dogs, even those "trained", to not charge and attack you. They are animals that are triggered by microevents our human brains cannot perceive. Do not take the risk of relaxing near an outsider's dog and not know how to defend yourself and your loved ones. Remember that even veterans in dog training, behavior, and psychology have to fight off dogs. We are simply human.