my dog has similar traits, except he won't back off. He snaps and growls if we reach in or touch him while he's eating. He clearly is an alpha dog but we're kinda outta ideas. He went to training school when he was 1 but hasn't helped his aggression.

 

The spray idea works really well, but you're not supposed to really show that it's you. aka, hide the bottle behind your back after you've sprayed him inconspicuously.