Shake-Away Deer Repellent work by manipulating the deer's inborn instinctive fear of predators. The active ingredient in DRPs is predator urine. The scent of the Coyote's marking tool (urine) communicates through the deer's most keen sense, smell, to alert the animal that danger is lurking somewhere nearby.
With your yard or garden marked with the scent of the predator that deer fear the most, your area becomes the spot to avoid on the deer's normal browsing routine. Over time, deer will alter their normal route in order to avoid the risk that your "predator" represents.