Hmmmm. I actually work for our local SPCA, and am a huge cat lover as well as chicken lover!
The best piece of advice would be to turn your coops into Fort Knox. Don't use chicken wire, opt for the more durable (but a bit more pricey option) hardware cloth. Put this hardware cloth over the windows as well, so it acts like a screen. Be sure there is a roof to their run as well.
Do you know when the cats usually come around? You could set up sprinklers in the area at those times. One thing I've learned about free-roaming cats is that killing them is NOT the answer! When they're taking out of the environment, it acts like a vacuum, and more cats come it to take the vacant spots throughout the community.
See if the cats are fixed. If they're not fixed maybe educate the owner on the importance of fixing their cats, and how it would (majority of the time) reduce the wondering/roaming from home. This is b/c their hormones won't be driving them to find a mate, and "Oooh look! A chicken!"
I wish you the best!