It is unlawful for any person owning, harboring or having the care, custody or possession of any dog to keep or maintain such dog in any place in the corporate limits, unless such dog has been vaccinated as provided in this chapter. This section shall have no application to dogs under the age of four months, who are fastened securely by a rope, chain or leash, or confined within the private property of the owner or person having control of the dog. (Prior code § 4115.1)