Shoo Shoe

Many dogs have no sense of whether or not to approach a person: sometimes they will get patted, sometimes not, individual stances can probably not be read well enough by the dog to know the outcome in advance. Some people are truly frightened by dogs, some simply fear to be slobbered by an especially enthusiastic dog. Dog owners usually fail to react as well.

So i propose a shoe add-on (inlay, or small screwlike object to be fastened in the sole), that emits a distinct ultrasound sound while walking normally - thus a dog can detect any wearer of such at a distance. If the wearer feels threatened by a dog, or simply wants it to clear the vicinity, a simply grinding motion with the heels emits a far more powerful ultrasound noise, uncomfortable for the dog. Thus, the dog can learn in it's own terms which humans are better left alone.