Ultrasonic Bark Stop
I was a bit sceptical about these devices, but a few reviews else where said they were good and it had a guarantee on it so I figured it'd be worth a shot.
This wasn't for my dog, but a pesky neighbours dog that barked constantly. I turned it on and tested it and my dog came running from the next room with its tail between its legs (sorry boy). I set it up outside for my neighbours dog but this dog needs serious behaviour training, I saw it triggering and the dog reacted, but kept barking anyway.
As with the guarantee, Bark Control gave me their address to return the parcel and made it a really easy hassle free process. They're based near Brisbane so it was all very fast (I got next day delivery and return was processed same day it was received) really happy, will return for other pet needs in the future!