§ 6.4.4. Survey monuments.Concrete monuments with aluminum or brass marking shall be placed at all corners of the exterior boundaries of the subdivision being developed and shall be set flush or up to six inches above the finished grade. Existing permanent monuments, which in the professional opinion of a registered land surveyor, or the city or county engineer are of sufficiently durable construction may be maintained in lieu of a new concrete monument as described above. All other street or lot corners or angle points and points of curve in each street shall be marked with an iron pipe or surveyor's marker at least 24 inches long and driven no less than one inch or up to six inches above the finished grade. All such monuments shall be properly set in the ground and shall be approved by a registered land surveyor prior to the time of final plat approval by the Planning Commission.