It is not too late to correct this behavior. It is not going to be a quick process and will take work. You will be using the techniques that we use with pups and they are proven to work. You just have to take it a little slower and start differently since Shata has already developed the behavior and had it a long time.
Many owners are able to help their dogs overcome this unwanted behavior with lots of patience and hard work. The following sites go over this in great detail. The last site give many different ideas and techniques to help resolve resource guarding.
If you have taken the time to read the above sites you will notice that the owners gained their dog's trust by not taking things from them unless they gave them something even better. In the case of food, I've found that hand feeding gets the dog used to you being around the food. Hand feeding can help in these cases, so I recommend you talk softly to him when hand feeding and you might want to pet his back as well, so he gets used to you touching him when he is eating . I usually progress to putting the food in the bowl and just hold the bowl continuing to talk and pet them. Once the dog is used to this, I will put the empty bowl on the floor and put food in the bowl piece by piece if necessary, so the dog knows that I control the food, not him. Additionally, you might have some really tasty treats in hand and as you get close to the dog start dropping these so the dog is associating your with giving more tasty treats rather than just approaching his food. Try hot dog slivers and raw liver. Once he sees that you are adding food to the bowl and not taking it away, he shouldn't feel the need to growl at you to warn you away from his food. At this point, you want to have an extra tasty treat like hot dog slices and have them in one hand to distract him from his bowl. As he takes the treats, lift a handful of food from his bowl and then put it right back. Be sure he sees you put it back. This teaches him that just because you take the food doesn't mean it isn't coming back.
I start taking food away from puppies and giving it right back when they are just puppies. If you frequently take things your dogs enjoys but are dangerous like cooked bones, stinky socks, etc, without giving something better in return, you dog might think that you are planning on taking his food away. You can use the leash to provide some negative reinforcement such as a quick tug and firm low toned "NO" when he growls, you also need some positive reinforcement when he is acting the way you want him to. The same technique should be used for toys, but use a "higher value" toy to tempt him away from a toy he has. Higher value toys are ones the dog likes more.
Most dogs would prefer liver or hot dog slices to bones, so those can be a good tempting treat to convince your dog to let go of a bone. Remember that initially you will be praising him for giving up the bone and giving it right back so he sees that non one wants to keep the bone. It will need to be an ongoing training exercise and may take months to stop the undesired behavior. Food usually works to get them to used to giving up non food items.
I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below.
In addition, if the situation is not improving using the techniques on the previous website, you may have to consult a professional behaviorist. You can usually find a behaviorist by asking your Vet for a recommendation or you may be able to find one using the following site.
Resource guarding is dangerous and best addressed by an in person behaviorist but many of my clients have used these techniques successfully.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer.