Deaf dog aggression

I have rehomed a deaf Bull terrier. He is a happy dog, really laid back and is fine in all aspects except when asked to leave a room.....He does go but turns and snaps on his way out. This only happened up to today on leaving the kitchen but this morning he got into the shed where I was cutting up meat for him (and my other dog) I asked him to leave which he did but then stood outside and was barking/growling and showing his teeth. I put a box between myself and him and shut the shed door with no bother. I realize I should have avoided the situation by shutting the door behind me so he could not get in but at the same time this does not address the problem. It's almost Jekyll and Hyde traits, as he is fine in other aspects and even to give food to does not snap or grab. I have not made a issue of it, being deaf I cannot reprimand him by voice and I have a stop hand signal but don't want to approach him with this when he is in this mode. I will try to get a behaviourist onto this but at present it would be too expensive. What I cannot work out is whether it is a food issue or dominance one OR has he been mistreated in the past i.e someone skelping him when he would not do as asked and being deaf he may not have had the initial warning of sound we would give a hearing dog and felt he was being attacked? What seems strange is that he leaves then gets aggressive. Any ideas on this from anyone.

As you say, you don`t know what has happened to him in the past, so he will need time to allay his fears.
Please forget all the stuff you have heard about dominance. This is based on discredited theories and is not applicable to a frightened recue dog.
You don`t say how you are asking him to leave. Have you taught him a `go to` command? Or a Settle` command? Both entail the dog being rewarded for going to a particular place - in your case this could be just outside the door? To teach it, show him where you want him to go with a lure and reward when he`s there. When he gets the idea, add a signal.Increase the distance but keep rewarding.
He doesn`t know you want him to wait outside for his food. To him you are rejecting him / chasing him away. That is a terrible thing to a dog, so I`m not surprised he is reacting badly.

Hi there, thanks for that. I basically just point at the door and he does leave I don't crowd him or chase him out it's just strange (to me) that it's when he is actually going or already out that he turns and shows aggression. As you say I will from now on make him wait outside, which to be honest he was doing up to now it's just that he sneaked in and I did not see him. My other dog stays well away from the shed. I just prefer to be able to safely come and go without the fear (mine!) of the aggression. I do suspect that he is being a bit fearful of my reaction as he does actually go when asked now. Although this is a rehome/rescue dog he was obviously well cared for and has hand signals he responds to. I do wonder if this might be the reason he was rehomed! As the behaviour only comes out now and again, perhaps someone did not say and the kennels would not have put him in any situation where it would show. Guess I will never know. I have an 11yo son who I have told must never go near the dog on his own, it's just always a worry. I do intend to keep the dog as I don't think he is a danger I will just need to be more vigilant with him.
Thanks for your help.

Some Dogs with sensory deficiencies respond with aggression when they are in certain situations. I knew a dog, blind in one eye, who would snap at (not bite) if you approached too fast from his blind side.

Many people with deaf dogs use vibrating collars to get their dogs attention. You can also "clicker" train this dog with a light or laser (do not point it at its face)

Barry Eaton has done a lot of work with deaf dogs, I'm not sure how much the rescue has spoken to you about how to train your deaf dog so I don't want to repeat training techniques, but it's worth checking out his site and I'd recommend his book 'hear hear'.

http://www.deaf-dogs-help.co.uk/