What is dog repellant?

Dog repellant is a type of substance, typically sprayed on with an aerosol can, that creates a smell that is highly undesirable to dogs. It is heavily used by mail carriers, for example. A popular brand of dog repellent is Halt! brand.

Another approach to having dogs leave you alone is to use an ultrasonic-based system. Instead of spraying your body with chemicals, these devices work by means of a battery and a small emitter which produces a sound that humans can't hear, but which annoys dogs. These devices can be quite annoying to dogs and therefore can achieve a similar effect.