My Ancestor John Mulligan orginal home farm is one...

My Ancestor John Mulligan orginal home farm is one of the 4 first to become the Ex Farm, there is a monument - large but no one can find it, I walked 3 km and twisted my ankle doing so, and still have not found this large monument for my 2nd Great GrandFather. Has anyone got any idea where it is - I have called every phone number I can find and no one has any idea where it is or even what I am talking about, Anyone able to help ?