Rescued dog aggression

My wife and I adopted two 10 year old dogs about 18 months ago. One is just sweet. They other is a sweet dog normally, but after about 8 months started aggressively guarding toys and rawhide chews, etc. She's fine with no toys and with her food bowl, will even wait until told she can start eating... But if you get near or take away a toy she'll growl, lunge, snap, and be pissed off for hours after you've taken it away.

They both love to chew, so I feel bad about banning toys entirely, but the resource guarder is getting worse.

Any ideas appreciated. This is the first time I haven't raised a dog from a pup and don't know how to teach an old dog not to bite my hand off.