barking dog

So people keep calling the police  and complain that my dog is barking all the time. My dog is 12 years old and maybe once in a while she will let out one bark when she goes outside and other than that she just barks inside the house. We trained her to bark because our neighborhood is known for robberies so we want a dog that will bark at an intruder if needed. Well anyway we have already had a police and animal control visit but they found that our dog was fine and it was probably a different dog that was barking. Well now we have received a $500 fine because people keep calling the cops and blame my dog but how can these people sure that it's my dog that's even barking? Every house on my street owns a dog and they all bark. Should we fight the ticket or just pay and move on? Or what did anyone else have a similar situation?