Would a large RubberMaid tub do the trick? Basically the mice are just chewing through her bags of grain and helping themselves.
I would get a metal garbage can, I've heard those do the trick, but I don't know where you're get one of those...
I think these mice are basically partying in the tack room...There's mouse poop on all my stuff and they're sitting on my saddles to eat the grain they've stolen from Lacey's bags...as well as bringing seeds in from outside to eat, and leave the hulls of, on my saddles... Sneaky jerks!
The free food must stop!