Sorry I never came back, I don't usually check the rescue forum so I totally forgot to update!
I have class in a 15 minutes so I can't write out the how I taught drop it and bring it at the moment, but I'll be back later today hopefully.
As far as what to do when he does guard, I agree you should avoid eliciting the aggression as much as possible. I'm sure you have a decent idea of what he guards so don't try and take it from him or touch him while he has it and don't give him objects (unless you need to like his food and some toys) that you know he'll guard. Not to say you'll never be able to of course, that is what the other training will be for. If for some reason he does growl at you because he has something and you didn't think he'd guard it or you didn't notice he had something I would listen and move away. Yes this does show a dog that the growl worked, I don't think that's a bad thing, growling won't put you in the hospital, it'll keep you out of it by giving you a warning. I have also found that responding to a dog's warnings (though I prefer to respond to subtler signs like freezing/stiffness/slow movements, whale eye, lip licking, really quick irritated looking head turns towards me, etc.) can make them trust you. They don't have to overreact to you, they know you'll listen, so they will not escalate into biters. But yes, you are essentially reinforcing growling, but in the end, when all the training has happened he won't be upset by your presence near his stuff so won't want to growl, sot he previous reinforcement won't matter. Most importantly you should be causing him to growl so rarely that you won't be reinforcing the growl very often.
I have to go now but I also have some ideas on what to do if you MUST take something from him, I've had to do that several times with Tucker and what I do works really well for him. So I'll get back to you later.
Thank you ~Dixie's Mom~ for my awesome siggy!