E-mail my wife about a book we have on Dominant Dogs. If I recall, they had a whole section on how to correct your dog if it is growling at you when you approach its toys/food/etc. I believe they had that listed as a fairly serious "doggy offense."

I'd send you the book myself, but I'm not privy to its whereabouts. I'm pretty much only allowed to know where the refrigerator, remote control, and video games are.