Hey Pulirules. Yes, resource guarding is a very normal canine behavior but of course unacceptable in a human home. Like everyone else suggested, you should try to contact a professional, one who is current and has experience with resource guarding.
For now I would take all high value triggers (anything that may cause him to guard) away. Even his food bowl should be put away for a few weeks if possible, while you re-establish the rules around these items.
He should also be working for every thing that he considers of value such as treats, toys, access to outdoors, furniture (if allowed)...everything comes at a price particularly for a dog who guards. You should be as upbeat, calm and happy as possible during this training process....that's the way it should be anyway..
FIRST
I'm going to assume that you feed him on a schedule. Take his measured portion at each meal and feed it to him by hand for performing behavior (sit, down, watch me..etc) you can give him different amounts by hand for each behavior. This should only take about 5 - 10 minutes for each meal and is great for bonding and improving obedience as well.
NEXT
After a few weeks you can re-introduce his food bowl. Ask him for a behavior, drop a few kibble in the food bowl (while it's still in your hand-not on the floor) and offer them for compliance. Do this with variable amounts as above for a fews day to maybe a week.
FINALLY
Place his food bowl on the floor and ask for a behavior, drop a few kibble in when he does what he's asked. Then pick his bowl up, drop a few kibble in and set it back down when he complies with another command. Ulternate picking the bowl up to add kibble with adding the kibble while the bowl is down on the ground. Make sure that you put your hand right into the bowl when adding the kibble each and every time.
These exercises should be a part of his life. Not to the extent as shown above but should be done a little with everything that he considers of value. Resource guarding can also transfer to different items such as toys, people, spaces so be watchful.
Make sure that you trade him for everything, even things that he steals from you so that he doesn't feel the need to guard.
A great book to pick up is MINE by Jean Donaldson. You can have it shipped from
www.dogwise.com and it's quite a small inexpensive, but invaluable book.
Hope this makes sense...let me know if I can clarify..