Fences four and one-half feet high, in good repair and so constructed as to prevent the escape of sheep, and any natural barrier equivalent to such fence shall be deemed sufficient, except fences on the sides of highways that the owners of land are not bound to make and maintain. Occupied land bordering upon highways shall be deemed to be the enclosure of the owner or occupant. A person driving cattle, sheep, swine, or other stock upon a highway, and exercising reasonable care, shall not be liable for damages by reason of the escape of such animals into an enclosure adjoining the highway, unless the fence between the highway and the enclosure is a sufficient fence within the meaning of this section.