Have used ultrasonic dog repellent for several years. It works very well, it will stop a dog in full attack. I live and ride in rural America so encounter dogs frequently. Does have a couple of limitations. It will not work if the dog is deaf and it is directional. You must point it in the direction of the dog. If there are dogs attacking you from several directions then it will only work on the dogs you point it at. My backup, is a collapseable baton. In olden days I would have used my frame pump but the baton is easier to get out and use and yes I have used it very successfully. I have to admit that most of the dogs I come across are just farm dogs that want to run along with me but there are more and more wild dogs around.