That all unused and abandoned wells, pits, mines or other excavations situated upon land not enclosed, upon complaint in writing being made by any citizen to the owner of the land or his agent whereon such well, pit, mine or other excavation is situated, shall be enclosed or filled up, or securely covered, by such owner or agent, within twenty days from the date of the service of said notice. If the owner or agent of such land shall not reside in the county where said land lies, then such notice shall be conspicuously posted upon said land for twenty days.