The prohibition contained in section 5-4-6 of this chapter shall not apply to the keeping of vicious animals in the following circumstances:
   A.   Law Enforcement: Animals under the control of a law enforcement or military agency.
   B.   Guard Dogs: The keeping of guard dogs. However, guard dogs must be kept within a structure, a fixed enclosure, at all times, and any guard dog found at large may be processed as a vicious animal pursuant to this chapter. Any premises guarded by a guard dog shall be permanently posted with a sign containing the words "Guard Dog", "Vicious Dog", or words of similar effect, and the owner of such premises shall inform the Johnson County sheriff's office, the mayor, or his/her designee, that a guard dog is on duty on the premises. (Ord. 1995-97, 11-14-1995)