Defeat the Bark: The Bark Buster
Have a breed of dog that barks all the time, and you want to quiet them down without yelling or swatting them? How about The Bark Buster ought to do the job quite well. From the site:
When your dog barks, this sonic unit emits a harmless, high-pitched pulse inaudible to humans, but extremely irritating to dogs. He soon learns to stop this unwanted behavior. Portable and water-resistant, it has two sensitivity levels and is effective from up to 20 ft. away. Use it indoors or outdoors, on its stand or wall-mounted (hardware included). Uses one 9V battery (not included). High-impact plastic. 5″ long.
You can grab this useful little gadget for $14.99 from whateverworks.com (new stock expected soon).