Where can i buy one of these my dog constantly barks when in the garden he loves running around but if he hears anything he goes nuts even at the birds flying past. When out on lead you never hear him and never barks in the house, even if i'm hanging out washing he charges around barking until neighbours shout

What you can get is an air collar, this is NOT a electric shock collar, basically what it does when your dog barks or go's nuts you press a little remote control and a sharp puff of air comes from the collar and startles your dog, therefore distracting it from whatever its barking at. My friend used one for her Wire Fox Terrier and it certainly worked, you could try that i suppose?
You can get them from most good pet shops.

Good Luck

Have you thought about rewarding him for the times when he is quiet rather than possibly scaring your dog? I have heard of dogs who when first squirted by 'the thing' have refused to enter the place where it happened - which can be very inconvenient....... Instead make sure he gets no attention for barking (try having a word with your neighbours and explain this is part of the training program as you know it is a problem for them ;-)) and make sure you reward him for those times when he is quiet, call him to you (ask for a 'sit' or other behaviour you know he already knows the command for if you don't like the idea of rewarding him for nothing) and give him a reward - he may well prefer you to throw a ball for him, but some dogs prefer a food treat - if he starts barking, he doesn't get any more reward.....

I just saw the other day on the Bensen Ltd website, www.benson.co.uk (look under the pet appliances) and you will find an anti bark/dog off product that emits a very high pitch sound that dogs don't like, at the touch of a button. (quite good really as it's an all in one with personal alam as well) You might find this better as i did have an anti bark collar for my noisy bitch and it was quite yucky seening her get a shock from the collar (it was set at the lowest setting - I don't like to think what the high setting was like, but mind you, she very quickly learnt not to bark!) But if I had to choose all over again, I myself would try the sound one first as it is much nicer for you to use and dosn't cost as much. The air one sounds good too though don't know the cost of this item.
Hope this was helpful to you.
:-)