It shall be the duty of the property owner's agent when selling either unimproved or improved real property located in the county, whether or not in a subdivision, or in the event an agent is not employed, it shall be the duty of the property owner, to disclose to the prospective purchaser, or if more than one (1) purchaser, to at least one (1) of the purchasers, prior to the entering into of a contract for sale of such property, the relative location of any airport or heliport, as defined in the county zoning ordinance, existing within a five-mile radius of the property. (1974 L.M.C., ch. 43, § 1.)