I remember the earlier posting. These are sick people.
You did check all the legal issues regarding keeping chickens in a suburban area, right? It is definitely legal for you to do so? Not just chicks, but full-grown ones? Your best defense here is going to be the fact that keeping chickens is legal, so if you have checked and it is indeed legal, get that in writing (in fact, you may need some form of license to do it anyway so that would be your proof). Have it always at hand in case they try to say you're doing something illegal.
And yes, build a privacy fence if you have not already.
I think that last time I advised getting some security cameras that record thiings and mounting cameras at the front and back doors and in places where you can see if someone has come into your yards or has been on your driveway, etc. You need to keep recordings in case these people damage your property; you need video of them draining the pool or pulling up flowers so that police can KNOW it's them. And definitely keep in touch and in good relations with all the other neighbors. If ALL the neighbors have issues with these people, you have strength in numbers to complain to the police as a group about harassment, etc. if it comes to that.
If you have not sought any permissions to have chickens, by the way-- do it immediately. If the neighbors are legally in the right and you cannot have the chickens, it is better to give the chickens to a farm rather than try to keep them against local laws. It would become a huge legal fight that would cost you far more than the chickens would ever save you in food bills.