i had that problem with my RB Dalmation.Most of her life she was protective of her rawhides/bones.She was VERY protective of it and we could never get near her.Every time we tried she snapped at us and growled like crazy! but the weird thing is right after she finished eating,she'd come over to us wanting to be petted,scratched,etc with her tail wagging like crazy!lol she was just protective of her bones.She didnt even like the vaccuum coming near her.lol.
Honestly im not really sure what to do.We tried to get our RB girl out of that habit,but she was too protective of her rawhide.You didnt fail,lots of dogs have problems with there rawhides even my RB beagle had a problem with it and could never get her out of that habit.
I would suggest what everyone else has said already.