Simply calling the city hall for the city manager is a start. Filing a complaint with the police department is another and if you have a humane society, inform them and ask for suggestions. THis will document it as a call for help from you that will be good if you get to charges.
The suggestion of taking photos is great.
Do not tolerate any one else's dog in your yard. Another thought, contact your home owners insurance to see what suggestions they have as well. The more you know and let know the sooner and faster the problem gets solved.
I was with the HS for many years and found this was great tips given.