These rules appear to be "don't ask/don't tell" enforcement.
If one is bad natured enough to have bad relations with the neighbors (or unfortunate enough to have bad natured neighbors) then there can be problems, though the County is slow to react.
Back when we were keeping ducks, there was a neighbor who let their dog run free, and gave our ducks problems.
A number of people were irritated by the dog, and had no problem with the ducks, so when when Animal Control (an arm of the Fairfax County Police Dept) wanted to take the dog owner to court, they asked us as the duck owners to file the complaint.
Even though the ducks are not allowed, the judge in court made a show to the defendant that Virginia law requires owners of waterfowl to protect their flocks by force of arms (this was a bit comical in the courtroom because the law being cited was in a leather bound book about a foot thick, and the judge made a show of it, saying, "I'm not sure about this" - and nodded at the clerk -- a young petite woman -- who displayed obvious effort as she carried the book over to the bench -- and it was a setup, because what he was citing had already been bookmarked), and after the judge read the applicable portion of the law, he looked up at the defendant, and said, if I were brought into his court for having discharged a firearm in Fairfax County (illegal here) in the course of shooting your dog, I would have to find him not guilty.
The Animal Control officer whispered to me, "We told the judge your duck was a pet, and he was o.k. with that."
And the emu makes no sound that would bother the neighbors, so I am not anticipating any problems.