This idea came from DIY Maven (one of my gurus) on Curbly. It's a prescription bottle turned into a hide-a-key by super gluing a rock on top. Way less conspicuous than those fake-rock hide-a-keys, right?
With the amount of old prescription bottles I have laying around the house from the last year, I could line the whole freakin flowerbed with hidden keys. Or...I just had an epiphany. Look for homemade hide-a-keys coming your way next Christmas.