fear aggression or resource guarding...?

Question
Hi, I have a 18 month old beagle, terrier, cocker mix. I have had her since a puppy and have had 2 different trainers. One which trained her using the more traditional methods and then more recently since last November using the clicker training which I found to be much easier and beneficial to my relationship with her. Anyway, she developed this food guarding and aggressive behavior at about 6 months of age. Every time I feed her a meal sometimes she is fine and sometimes if I or my boyfriend walk by her she starts growling and quickly eating which sometimes results in her choking herself. We have tried so many different ways like hand-feeding her and working her way back to eating out of the bowl and then feeding her small amounts at a time and if she shows aggression we stop meal time and try later on. I am getting so frustrated. She is normally a very sweet dog, she does not mind people when they come to visit or if we go somewhere else, but she does not like other dogs if there is food or around or at times she can get territorial but it varies between the different dogs. When I take her to the dog park, she has no problem playing well with the other dogs. She understands basic training, but the food aggression really drives me crazy, Please help.

Answer
Don't stop mealtime - by taking her food, you are actually making her worse.  Her anxiety is that the food will disappear, and by taking it, you are confirming her fear, making her want to eat it or guard it.  You'd be better off walking by and dropping food IN to the bowl so that she would not perceive you as a threat.  I would advise you to grab a copy of Jean Donaldson's book, "Mine! A Guide to Resource Guarding in Dogs" and go through the whole protocol.  You are unlikely to be able to stop her from being guardy about food with other dogs, so it's probably best to feed her away from others.  But, you do want to get the aggressive behavior under control when it comes to humans.  You can feed her from a bowl that is designed to slow her down while she eats:
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