He'd had at least one treasure seeker get within 50 yards of the location, but didn't spill the information at that time.
Did he say "50"? If so, that's intriguing because the spiritual information stream that runs parallel is that one can reach "49" by human effort, but only God can allow access to the 50, hence the 50th gate of understanding, or the counting of 49 days toward the Law which was given on the 50th (yet not counted) day.
A distance of 50 units (length, time) equates with "you have arrived", especially after many challenges, tests, and obstacles.
The topic is a big "National" treasure hunt, after all. This really IS big treasure.
What are the odds he tucked the world's smallest violin inside, because there's always that somebody who will keep whining that it wasn't fair. :)