In regard to dog on dog resource guarding.... you could always practice some exercises where one person brings in the other dog on a leash into the room. At that time, the resource guarder gets high value treats and lots of attention. Then the other dog is taken out of the room for a minute or so and the resource guarder is ignored.... very boring when the other dog isn't around. Then repeat. Do like 6-10 repetitions and then come back to it later..... do it a few times per day. So basically, you end up associating the presence of the other dog with good things.... never punishment. The other dog has to be the sign that good things are about to happen. Don't even talk to, touch or look at the resource guarder in any way. Attention given to the resource guarder will reinforce the the bad behavior.
When you're not doing specific training sessions, save most of the love, attention, yummy food and games for when the other dog is around and keep things fairly boring. Of course you are still going to give one on one attention to the dog occasionally but for a while, just try to send the message that the other dog around is not a threat... but that the other dog MAKES good things happen. I wouldn't really scold at all with other dog around, because then it just pairs punishment with the other dog. You probably inadvertently have told him "No!" or scolded him or whatever when he does this and then taken the bone away. In his mind, he's probably thinking "Whenever this other dog is around, I get my bone taken away...." Dogs learn very strongly by association, so be careful what is paired with particular behaviors. Heavily correcting a dog who has guarding issues is entirely counter productive. The guarding stems from FEAR of losing the item in question. Correction just reinforces that fear the dog had. Of course, I still think anything high value should not be left out if dogs are not supervised.
The other thing I would recommend for a resource guarder is building up their confidence and trust in you with other activities like obedience or agility training. Part of the issue with guarding is that the dog lacks trust. Training in other areas really helps to build trust.
Oh, I've heard great things about this book: Mine! By Jean Donaldson, you could check that out.
