Relax, this is what you do.
Get a pile of wood ready as an obvious pile to steal from. Take a few split chunks and remember which ones they are. Get a couple .22 LR shells, drill the wood pieces and drop in the ammo, seal it up with wood putty. Imagine their suprise when they burn it! might even help you figure out who the thief is.
22LR? If you're going to do it, do it right. Pack about an ounce of 4F Black powder in the hole. Your luck, they'd sell the load to some poor widow woman.
Ian