has anyone tried an ultra sonic bark collar that lets out a high pitched noise only the dog can hear if it barks? also there is one for the garden which is meant to prevent barking for 50 feet. do they work? the collar devise looks quite big and i suppose it has to stay in the excact place on the neck or it wont work? i have 2 dogs and would hate it if the wrong collar went off. any advise?

That is exactly what will happen!  My advice would be to steer clear. Teach via treats, yes it takes longer but is soooooooo much kinder and rewarding for yourself and your dogs.

I'll admit to having tried both. Both were totally ignored.

I bought the one that lets out a high-pitch noise. However my dogs never wore it!
My brain-wave was, which worked, that I lay it on the floor at the stairgate, which is where they gathered and barked. It worked a treat.
It has never really worked much, and have never replaced the battery,because all I have to do is lay it on the floor(not working),and they take one look at it and dont bother barking!
It changed my life!