Anyone ever use an electronic "dog chaser device" to deter aggressive dogs?

Try an air horn. One of the small ones that they use for sports games. It has a very loud and annoying noise the dog will want to get away from. There is another product too that they sell at Petsmart that helps scare off dogs. It's kind of like a repellent spray that sprays citronella at them. I can not remember the name of it right now though. The workers could point it out to you though.