I have been similarly "obsessed", but have not found it. The circled area on the map below shows my current "best guess" as to the location. I can provide an explanation for that if desired. (Ignore the "x", that was something else). If your friend is willing to share his ideas with me as well, I'd appreciate hearing them.

Regards,
Terry
Email: dev...@chebucto.ns.ca
Boundary Rock is one of a handfull of Grandmother Rocks to which the Mi'kmaq have ascribed spiritual significance from ancient times. It is located along an ancient portage route and is near the "height of land" between a surprising number of separate watersheds.
When the Colonial government of Nova Scotia decided to divide the Province into a number of counties, it chose Boundary Rock as a legal boundary marker, junction point, for Annapolis, Yarmouth, Shelburne, and Queens Counties. (Digby Co. did not initially exist, it was part of Annapolis).
There are a number of photos in archives from around the start of the 20th century that show hunting/fishing trips, accompanied by Mi'kmaq guides, posing for photos at Boundary Rock. The monument was covered in graffitii even then, including some Mi'kmaq hieroglyphs/ideograms. Be careful about the archive pictures labelled "Boundary Rock", as some are mislabelled and actually show a different stone with Mi'kmaq hieroglyphs/ideograms.
Later, the legal junction point of the counties was moved. Actually, it was moved a few times. Most people seem to have forgotten the actual location of Boundary Rock, and no one I've talked to has claimed to have located it, but many have claimed to have tried. At least one failed attempt was made by helicopter.