You might give the Dog Dazer a try. It produces a discomforting but not harmful high powered sound, audible to dogs but not to humans. The website below must have the shipping weight listed wrong because its light, I think the 9volt battery weighs more. Worked great for me until I dropped it on the highway on one of my rides.
Put dog dazzer on a search engine and you might find a better deal.







http://www.shopfromyourhome.com/Merc...duct_Code=DAZX