[KazzyK810]

I don't know what the "proper" way of training against this is...I just know what I've always done. Just like I handled my pups feet, ears, mouth frequently from day one, so she was used to it when needed for future grooming activities, I've also made it a habit to move her food bowl slightly and/or pet her while she's eating, take her chew toy or bullystick after she's been chewing on it for a while, only to pet her & tell her good girl and the give it back, so that she didn't become snippy.
Getting my last yorkie when my kids were quite young, I was very conscious about doing such things so she was used to it. I didn't want her snapping at my kids if they walked by her while she was eating or if they petted her while she was chewing on a favorite chew. It worked great with her, so I do the same thing with my Current pup, ZoE. But even after working with her on this, there was a time a month or so ago where she growled at me when I took her bullystick away at bedtime. I made it a point to give it to her and take it away multiple times throughout the day for the week following that incident. Now, she's not aggressive/protective with them anymore. I think that training is an ongoing process and requires periodic reinforcement. I don't know that there's a quick fix that is permanent.
I'd be interested to hear how others have dealt with this issue.