Get an ultra sonic dog trainer and use it every time it barks.
Otherwise get your own, louder dog.
They're very hit and miss, I could spent 30 quid and wire one up to the wall outside and have it not work.
And, although there's a few flippant remarks in this thread, I want to stay in the right, so no poisoning, no revenge noise-making etc as knowing my luck, it'll be me that ends up in court on the wrong end of the law.


