Hi Acamper, a book for reference with regards to this I would reccomend is, "MINE! - A PRACTICAL GUIDE TO RESOURCE GUARDING IN DOGS". Imo-Resource guarding in its very simplist form can be considered the dog protecting its food. Mastiffs are known for resource guarding or owning an object, which in many ways makes them great for the use of property protection. But to me, when a dog resource guard's there was a step missed by whom ever raised the animal, again that is only because I would clobber a dog in my house that ever did this to say...My 6 year old. I teach my dogs from the earliest age that everything is mine and my families, then after (if they are lucky) they may have it. I may sound "mean" here, but there are reasons for it. I have seen what can happen to a child if a dog is allowed to resource guard. I have also had the call from a puppy buyer needing stitches from a five month old, because it was allowed to resource guard. Your dog will only do...What YOU the owner excepts and allows. But to me, fear based responces are Even more nerve racking...More dangerous and difficult to work with. LOL, which again typically I blame on the owner. Hope this helps!