The owners, contract purchasers or lessees of lands, lying next to the exterior boundaries of any such herd law district, may construct a legal fence along the whole or any part of such exterior boundaries including the intersection with the roads which enter such districts, provided they construct automobile runways and cattle guards and gates in such fences where same cross such roads, according to plans and specifications approved by the state highway engineer and such runways, cattle guards and gates when so constructed, provided said gates are closed, shall not be construed to render such fence not a legal fence.
NMS § 77-12-9