No person who owns or occupies land shall knowingly allow any well which is within 500 feet of a dwelling or within 200 feet of any highway to remain open on such land, unless there is around such well a substantial fence or protection at least 3 feet high so constructed that no child can crawl through or under it. Any such well shall be deemed to be open unless it is protected by a covering strong enough to hold 1,000 pounds and secured so that it cannot be easily removed by children. The term “well” as used in this subdivision shall mean any artificially made hole in the surface of the earth (a) which is more than 4 feet deep and (b) which is more than 8 inches in diameter and less than 16 square feet in area at the top and (c) the sides of which are steeper than a 60 degree slope.