A monument shall be accurately placed at each corner and at changes in direction of the boundary of the subdivision, in boxes, at each street intersection, at points of curves of streets, and at intermediate points as may be required by the City Engineer. The tops of the monuments shall be set at the finished grade upon the completion of the grading of the streets and lots. Iron pins shall be set at all lot corners. If monuments are not installed prior to recording, a certified check shall be deposited with the City in an amount to be specified by the City Engineer; this check shall be returned when monuments are installed according to plat requirements.