Self defense foe dog attack

Is there a reliable produt that can deter a dog attack? I frequently visit my local park for walks, and I’ve witnessed close calls with dog attacks. These incidents mostly involved pet owners who didn’t keep their dogs on leashes and then aggressively approached someone. I considered purchasing a retractable self-defense baton, but I’d prefer to avoid causing any harm to the dog. Is there a legitimate spray that could be used to deter a dog from advancing?