I guess if it’s city ordinance then that would be hard to get anything done via the courts unless you have deep pockets for legal fees.
I’d hammer on the mayor and town council about changing their ordinance. Be a damn shame if a bunch of negative press started to get around that they passed an ordinance that allowed the dog owner to escape accountability. Social media and the local papers would be a good place to start. Might not help out your situation but could lead to helping someone else out down the road.