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Okay, well you could always build one that emits a high frequency noise, sort of a dog wistle, If I remember correctly a dog can hear a frequency up to 40,000 Hz, and humans can hear up to 20,000 Hz. However I would suggest building it in the high 30's, as some people like me can hear slightly into the ultrasonic band, and it can be quite painful. So I'd only suggest this if you don't care if the dogs gets hurt.
The only other problem with this is that you may see an increased number of insects in the area if you leave this on as it will also drive away most predators, and especially bats who's main food source (brown bats that is) is insects, and who are sensitive up to 100,000 Hz. It drives them away because it confuses their senses and all but blinds theim from using echolocation which is their primary sight, and used in hunting. (I wonder if they can listen in on low frequency radio stations, have to look into this.)
Me personally, I'd just invest in a garbage can with a solid lid that takes a good bit of effort to open.