Resource Guarding

Resource guarding is an issue with so many rescue dogs. Some may have had to fend off other dogs in their previous homes in order to get their fair share of food where others may just have never learned to "share" with humans. I've had my share of fosters with resource guarding issues (Arlo was one of the worst...the Min Pin in the picture) and I have "cured" each and every one of them.
My American Pit Bull Terrier came to me with resource guarding issues around bones/rawhides. I had already worked with him enough to know that he had great Bite Inhibition so I wasn't worried about working with him. Trying to establish "dominance" or become the "Pack Leader" by using force can get you hurt...especially in resource guarding cases. When you don't know if a dog has Bite Inhibition, be careful and go slowly.
When a dog guards his food bowl, leash him to something (couch, kitchen table, wall, etc) while he eats and put his food bowl at the end of his leash line. By doing this you can avoid getting bitten by him lunging at you while he is eating. Approach slowly and toss a little piece of cheese or freeze dried liver into his bowl (TOSS, don't not bend down and place it in the bowl). We want him to learn that a human approaching his food means something better is coming and not that we are going to take something away from him. I would do this throughout each meal for a day or two depending on how fast he progresses (longer if needed). Even if he growls at you while approaching, still toss the bits of cheese. We want him to build the association of human approaching = cheese raining down from the sky. Progress slowly with this. Most dogs learn quickly that when you approach, something better is coming so you can move on to the next step. The next step for me would be to reach down and place the cheese into his bowl several times each meal, walking away and re-approaching each time with the cheese. The next step after that would be to pick up his food bowl, put the cheese into it, then place back on the floor for him. Remember to have him leashed for each meal to keep yourself safe. Progress slowly and watch his signals (is his tail wagging and does he looked relaxed or are his ears back and he is growling?). If he's not ready for you to pick up his food bowl, then go back a step or two. It's about building trust so don't push him too far too fast. We want him to think that when we take something from them they always get it back and most of the time we have added something even better to what he already had.
I started this training with one of my dogs when he was 10 weeks old and I have seen him allow an infant to crawl up to him and take a Bully Stick right out of his mouth. Experience taught him that he will get the "high value" item right back so there is no need to panic. My APBT was six years old when I got him (less than a year ago) and he will now allow anyone to take anything from him without any growling at all. He also now knows that anything taken from him will be given back to him so there is no need to react...he just stares at me with his big goofy eyes and waits for me to return the item to him.
Resource Guarding can be scary especially when a dog is new to you. Proceed slowly, build trust and before you know it, he will be all wags when you approach him while he is eating anything.