Think of it this way:
Suppose you were really hungry, and you sat down to eat. Just as you did, someone comes along and starts messing with the things on your plate, interrupting your dinner.
This may be just fine on most days, but there will come a day when youa re gonig to look at that person and say "if you touch my plate again, I'm going to kill you." Same for your dog.
Now imagine this. Suppose you are eating, and someone keeps passing by quietly and putting chocolate treats on your plate for desert.
Pretty soon you are going to smile when you see the person coming, because maybe they have a nice piece of something delicious to put on your plate.
Same for your dog.
I DO NOT disturb dogs when they are eating. Food and eating is a survival instinct in dogs. Messing with their food is, in their minds, messing with their SURVIVAL. Think of how dogs protect their food from other dogs. Caping their food. Freezing. Staring. Growling. They defend their food because in the wild, eating is surviving. Dogs retain these instincts. STOP messing around with the dog and his food when he is eating.
If you feel you have a real issue, then put the bowl away.
Hand feed this dog a handfull of food at a time for 4 days. No bowls whatsoever.
On day 5, put the bowl down on the floor, and put the food in handful by handful. Let the dog eat what is in the bowl before you put in more. Wait until the dog looks up at you for more food before you put it in the bowl. Feed this way for 4 meals.
Then after 4 meals fed IN the bowl, handful by handful, put the dog's bowl down with the food. 3 times during his meal, go up to his bowl, ask for his attention, and feed him a treat from your hand. At the end of his meal when he is done, go put one more treat in the bowl for him to eat.
Remove bowls and all eating paraphernalia immediately when the dog is finished eating.
For the next 2 weeks, pass by the dog's bowl 2 to 3 times per meal and drop in someothing really tasty. It has to be something really good, like cooked chicken, beef, cheese, etc.
This regimen will solve most dog's food aggression issues. I feed my dogs in crates or outdoors where they are not disturbed during their meals.
I do not find it necessary to hover over my dogs, or bug them while they are eating.
In addition, I play "trade" a lot with puppies. I always have a pocket full of treats. I trade treats for toys, bones, food, etc etc etc.
I NEVER reach for a puppy to take something away, I always extend a treat to trade, and AS they are spitting out whatever they have, I say out.
So puppy earns a treat, I get what he had, he's happy, and he's learning a valuable command: spit out what you have, and you will get a reward.