Aggresive behaviour with respect to food

Question
I have a three-year-old German Shepherd.  He is one of docile and passive animals I have ever encountered.  I recently had some friends over for dinner and they brought their young Beagle.  I have had Fritz since he was a puppy and I have only seen him act aggressively once (it wasn't really aggressive, he was defending himself).  I perceived him to be very well socialized.  The Beagle went straight for Fritz's food bowl and within seconds Fritz had him pinned on the ground by the throat snarling like some sort of crazed beast.  It makes sense that this is somewhat natural but it was unexpected and I was disappointed.  Also, I will be getting another dog soon and it worries me.  I would rather not have to feed them in separate rooms or at separate times.
Question:
How can I modify Fritz's behavior so that he does not turn into a savage beast when food is introduced into the picture?  

Answer
Hi Samuel
I feed sometimes out or a total of 9 German Shepherds, i will feed often 5 at a time, telling each one when I set down the food bowels which one is Gillion's, Gino's, etc.
They know my english and know I amd the BOSS AND LEADER so they listen for  commands from me only.
I am now baby sitting two males ntuered that do the same as they followed my instructions in their puppy kits given them.
Pups are only as good of adults as one makes of them and I stress this upon my customers needlessly.  U must be in control, use POSTIVE TRAINING methods and pet and praise when done good.
Food agression in my part is totally ridiculous as when feeing a puppy I make my hands part of the dish of food, petting the face, rubbing the ears, nose, moving the dish about but not taking it off the dog, just moving it about.
I have NEVER  had a food agressive dog or puppy as I work on this from day one.
there is absolutely no need for a dog to guard his dish in the first place why was it there with food in it at that hour?  A dog is fed twice a day and what it does not eat it is taken up put in fridge for next day to finish not sit and wait on the dog.
When a dog comes to visit there should not be any food in a dish only a water dish.  So, this was an accident waiting to happen because of you feeding improperly your pet.
Feed morning and late afternoon, what it does not eat in 20 minutes put away for next day or dispose if one can afford to do this.
It was NOT your dogs fault, it is territroial and guarding its bowel of food left, so forget about it and do not let is happen again because u left food in your pets dish unetaen. umodifiy its behavior by when it eats sit and rub his face, ears, nose, etc.  talk to him and let him know its no threat to eat and food be taken away.  same when u get another, feed together and be there while they eat and sit down with them each and rub faces, talk to them and let them know it no threat with food to eat.

Kind Regards and any further help let me know.........
Patt
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