"I think if there is still a chance the key is out there, it will have to be in a secure place, or at least one that had/ has very little chance of being altered. Even stone walls have been worked on."
Exactly. But what's a secure place that has very little chance of being altered? Anything out in the woods can easily be altered by flooding, trees falling, etc. And anything man made, which will be probably be more secure, can easily get messed with over 10+ years. And that's just the key itself, never mind any markers being altered. Look at the history of the Secret. Trees that were intended to be markers in the Chicago puzzle had been cut down in the 2 or so years between publication and when the guys first got on the trail.
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