We are using 4 seperate Electrical "gizmos" that supposedly emit a high pitched sound (above human hearing) that supposedly does not both our dogs. It seemed to work in my barn, and so we have put them inside the bus in 2 seperate locations (they plug into a normal AC socket and don't use much power) and put 2 outside to "surround sound'em" Hopefully it is working, we find no trace of them as we did in the barn. The barn is now clean and hopefully the bus will remain that way also.