This clue works best with many people, but can work with only two. The treasure hunters must be spread out across the house/garden in a chain, preferably where they can only see the person before them in the chain and after them in the chain. In the example below hunter 1 has the encoded message, and hunter 5 is given the decryption sheet.
Hunter 1 acts out the message one letter at a time to hunter 2, who acts it to hunter 3 and so on until hunter 5 can interpret it.