Harry,
I may be wrong, but I believe the eighteenth "monument" is actually the final location on the Stone Maps. If you have followed the maps (precisely) to the "ILR", you are, for all intents and purposes, at the final location of the maps. The question now, is: What are you looking for?
Do you believe the final location, #18 on the marked trail, is different than the preceding seventeen places?
Having spent the last six years in that area, I believe you and your team are now hopelessly lost.

It is also possible that my team and I are the ones who are lost.
You have pointed out that your rock "carving" is actually "a hole within a circle". Why do you suppose that it is different than what is depicted on the Stone Maps? A hole would have been easier to carve than a small circle within a circle.
Since Wiz does "concur" with my opinion concerning what to do about going public with your "ILR", I may need to rethink my position.
Carved rocks are a time honored tradition with many people. In the early 1400s the Chinese Emperor, Zhu Di sent his most trusted eunuch, Admiral Zheng He and a fleet of one hundred Teakwood Junks, each around 480 feet long and 180 feet across, on seven trips into the lands of the barbarians to demand tribute and establish trade relations. In many of the lands they discovered on their trips, they left carved stone monuments as evidence of their accomplishments. It is likely that they circumnavigated the globe
two times on these trips. They did not leave out the Americas in those travels. On Zheng He's return from his final trip, all?... records of their travels were destroyed by the new emperor. A number of the carved stones have survived. The story is much more fantastic than our legend of the LDM.
Respectfully,
Joe