we have tried,but it seems to me dogs that dogs with temperments like sam rarely change
IMO that attitude right there is part of the problem. I'm sorry if that comes off harsh... I'm not trying to sound mean... I have a dog that is really reactive to other dogs. I would be lying if I said there weren't ever times where my attitude drifted to the thought that, "OMG he's never going ever get better around other dogs," but I have to remind myself that I need to put my faith in him and really give him the training he needs to overcome it. He may not overcome it, but I'm going to give it my all to work with him on it. I know how frustrating it can be, but hang in there.
There are going to be some dogs that wont change, even with the most extensive of training... but don't throw the towel in just yet. He may always be aggressive... but there are many people on this board who have dogs that are dog aggressive. I hope some of them will see this thread and offer you some better advice. You need to see a behaviorist first and foremost in my opinion. I cannot stress enough how important it is that Sam see a behaviorist to be evaluated. Aggression is a serious thing.
If you want Sam to overcome this then it is going to require a lot of work on your part. I wish you the best of luck. I'm anxious to hear others responses. Chaz is a great place to find some amazing advice.