A fence separated the 2 properties for decades. Both property owners presumed it was the correct boundary between the properties. There was never a dispute until a survey were done. Then neighbor found that 15% of their property was on the wrong side of the fence. A law suit ensued and the parties argued the doctrine of agreed boundary.
To have a binding boundary agreement, the following must exist: “ an uncertainty as to the true boundary line,  an agreement [to resolve a dispute] between the coterminous owners fixing the