Welcome to BYC. I'm glad you decided to join our flock. What kind of chickens are you getting? Cats are normally not a problem with the adults of large breeds (of course there can always be an exception), but with the smaller bantams or young chicks, they can be a real problem. Besides dogs and cats, rats might be a problem as well. Anytime you free range, even in the middle of a city, you run a risk of losing some of your flock. I would definitely advise locking them up securely in the coop at night. Please feel free to ask any questions you may have. We are here to help in any way we can. Good luck with your flock.