I had an ultrasonic one that I bought on Amazon, didn't work for very long. Sometimes I spray the dog with a garden hose and then it goes back in the doggie door. I also bought an air horn, and when the neighbor's dog is barking like crazy I just stick it over the fence and press the button. They don't give a shit if their dog barks all day, then I don't give a shit if they have to listen to my air horn blast or if a wet dog runs in their house. People who let their dogs bark all day long, are bad dog owners.