I've dealt with many highly food aggressive dogs all adults . The thing to remember about this is these 2 behaviors are related to the dogs survival instincts . Because these 2 behaviors are usually deeply set in adult dogs they are very difficult to deal with directly . IMO sometimes this is a dominance related issue and sometimes it's just a strong automatic instinctual survival reaction , nothing personal , dog just wants to get his food to survive .

I'm a K9 Handler and handle a VERY rank , handler aggressive and food aggressive GSD . I used to be a trainer in my K9 unit until my divorce and I needed more time with my kids. With my dog I tried months of hand feeding progressing to putting food into the bowl while holding it and allowing him to eat out of it while I held it , to putting the bowl on the ground and bit by bit putting food in the bowl . He was fine when I had the food and he knew he had to be calm to get it . As soon as I progressed to putting the full bowl of food on the kennel floor alone it only took a couple of days for him to revert back to his food guarding . It wasn't a suprise to me I did it more in hopes that it would improve our relationship related to his handler aggression . He came to me as a 2yr old handler aggressive dog . I was hoping it would solve his growling but knew it was a long shot .

My routine now is alot like yours and many others here . Put the dog in a down or sit , put his bowl of food in his crate or kennel ( I use both )release him from his sit/down and leave making sure nothing comes around him while he's eating . Return when he's done and remove the bowl . The whole time he's growling and slobbering .

Now with my dog I believe it's related to both dominance AND a strong survival instinct. Because I choose not to deal with these 2 behaviors by trying to extinguish them doesn't mean I'm allowing him to dominate me . I simply choose my battles . I deal with it by making sure he has a secure place to eat and noone gets around him while he's eating . I handle his dominance by doing consistant obediance , calmly and consistantly correcting disobediance right away not after multiple commands . I also don't allow him to get away with dominant behavior once he's away from his kennel or food .

My point in all this is you can deal with these 2 issues without having to extinguish them and still be the pack leader and have a very well behaved obediant dog . Mine is very controllable on the street and also does very well in competitions .

Go back to how you were presenting it and make sure the dog is allowed to eat in peace . Then make sure you maintain his obediance and good behavior away from the food and kennel . Qualified professional help can't hurt at this point but I would for sure get help if his behavior get worse away from the kennel . Also make sure you behavior hasn't change because he growled at you . He could easily pick up on your fear and get worse . Continue to be calm and consistant in your handling of him and don't take it personal and let it effect your relationship with him .

As for having him fixed . Usually in my experiance having an adult dog fixed has very little effect on his behaviors since they are all pretty much set by then .

Put the dog in a down or sit , put his bowl of food in his crate or kennel ( I use both )release him from his sit/down and leave making sure nothing comes around him while he's eating . Return when he's done and remove the bowl .

I deal with it by making sure he has a secure place to eat and noone gets around him while he's eating . I handle his dominance by doing consistant obediance , calmly and consistantly correcting disobediance right away not after multiple commands . I also don't allow him to get away with dominant behavior once he's away from his kennel or food .

If a dog growls and I dont want him to growl then he isn't going to growl. End of story.