I've had chasers turn tail when I woffed like a big dog. That gave me the idea of a whistle. An emergency whistle works around 50% of the time, the dog will run away. Sometimes, they will pause. I don't carry lethal backup and doubt I could access a concealed device in time whereas spray is easily put on the bike near your hand. Dogs are not a problem where I live but not in other states like NC, SC, GA, Ky.....etc