Crating - get a copy of Susan Garrett's new dvd (or VHS, I guess you can find it in VHS) "Crate Games". Start retraining with a different type of crate (if you've been using plastic, start the crate games with a wire crate. I would not suggest soft crates for obvious reasons)
Have you had his thyroid checked? In order to modify behavoir, you MUST make sure the dog is sound and healty.
Go to dogwise.com and look around for a good book, or two. "Mine" or "Fiesty Fido" come to mind. Also one of Dunbar's books/video address resource guarding, but I don't remember which.
Leave a leash on. Go buy a cheap nylon leash and put something yucky on it - bitter apple, deodorant, vick's vapor rub, palmolive all come to mind. You may need to rub it on every day, maybe twice a day. Do not put the leash on with a corrective collar (ie - choke chain). The problem is, if he bites you and you back off or escalate, you've just made your mountain 10X bigger.
Make sure he's getting enough exercise - physical AND mental. My young dogs (Zpuppy and the malinois) have most of their dinner in a food/puzzle toy. I really like a lot of what's in Control Unleashed. I think, especially if you see behavior problems other than resource guarding, the mat work is great for impulse control. The mat work is based (or is?) on Dr Overall's relaxation protocal. I'm wondering if you will start seeing issues in other areas. And my guess would be overflow behaviors would be related to impulse control. (I wonder if anyone has related resource guarding to impulse control. They seem related in my mind.)
Start teaching him to switch for higher value foods. While you are doing this, don't react if he gets hold of a high value food unless it is toxic to dogs (chocolate and the like). You need to know his hierarchy of values.
If you feel like you are way in over your head, recognize that. It's okay. If you don't feel comfortable learning from books/dvd's. That's okay too. Different people learn differently. Find a good positive trainer to help you out. That's better than wondering around in the dark.