This is a strange location for an Ontario Department of Highways Land Surveys marker. There was no provincial highway near this location. Far to the south at the edge of concession 2 (Ottawa Front, Nepean) is Robertson Road, once part of Ontario highway 15.
The disk tops a metal post above ground. To find the marker, climb over the guard rail on the north side of Timm Drive. The guard rail protects the steep slope above Still Water Creek. The marker is a short distance down the slope at the wire fence which parallels the road. In 2019, orange surveyor's tape marks the wire fence at the marker.
As expected with a Department of Highways marker, the unidentified marker is not listed in the CSRS (federal) or COSINE (provincial) database.