I've had four cockers, two working, two show. Of those both show and one working were gun shy- and I have to say in the case of our last working cocker, irretrievably so. He would only react to the real thing and not TV or sound effects. But the fear response was horrible to see. Dogs have a different hearing range so are often reacting to things in high frequencies not reproduced. Having worked for spaniel rescue I do know there is a small but steady stream of gun shy dogs being rehomed as pets only and I expect many things have been tried with them before they were given up. My feeling is that some dogs are just not meant to be around guns and you have to accept that. I was pretty glad of it too because I got one of my dogs that way, when he'd been labelled 'failed.'