I read this the evening you posted this, and then went to bed shortly after. Honestly, I had to check in with you as I haven't stopped thinking about the cat situation at your house! Are your chicks safe yet? You sound like such a sweet person as your note is so polite. I can't imagine confronting people about a pet that they leave go so carefree. We have a housecat, and also our daughter has a cat that we rescued from near death (this cat had anything & everything wrong with him when we found him outside by an old place we were at a few summers back...)
BOTH of these cats go CRAZY when they see any kind of bird out the house windows! I can only imagine what either of these cats would do if they had a chance at a small bird! Also, a friend of mine, pointed out a neighbor in her area who just takes out animals who trespass onto their property! YIKES! In some states it is considered trespassing and well...
I did do a google search, and not surprising there are a number of people who have the same situation as yourself and their chickens. Either a cat or dog, leaves/wanders from their own home and enters the chickens yard resulting in an attack on the chickens. One post even mentioned a motion yard sprinkler

that would go off and spray intruders when you are not around, like a motion detector light... not sure how that would work, and in cold weather climates one couldn't rely on that to work. I do KNOW Cats HATE having water in their faces though, but also are very intrigued with birds...
This summer I chose to approach a new neighbor of ours in which we found his dog running lose in our yard several times. I chose to walk over an introduce myself & our family which turned out to be a very worthwhile use of my time. My hopes were to explain our love/concern for our chickens safety, so we didn't have to later or possibly at some point confront them in grief/frustration/anger--- PRIOR to having something potentially awful happen!!!
After going through introductions and such, I mentioned our son had just began with chickens, lets them free range at times, and ...So, I told them that we have some concerns for their safety and such..... Well, immediately he told me that his neighbor growing up actually had chickens and HIS DOG actually got into their coop and killed ALL of their chickens! Well, the neighbor shot his families DOG, he told me! I nearly fell over!
SERIOUSLY! I asked him if he/his family were devasted over the shooting of the families dog? He said, when the neighbor came to tell us, my mom just said THAT IS what WE deserved! We need to take care of our pets. And they paid for the neighbors chickens!
Well, I was lucky on that one, and he went on to tell me that he would love to get chickens at their house too! He has kept his dog TIED up now, and he also just put up a coop with chickens of his own! YEAH!
However, we had a silkie chicken taken out by a hawk, nearly right in front of our eyes! So, even with that, can't always protect them!
Plus, our property has so many wild animals, we keep our chickens most safely in their run. Our yard backs up to a wooded/ county/ reforestation type of land which allows hunting during hunting season, along with hosts a fair amount of creatures naturally occurring. We are aware and have seen animals such as: raccoon, squirrel, deer, chipmunk, rabbit, bear, fox, snake, owl, hawk, skunk, eagle, opossum, to name a few!
I wish you the best of luck, and hope your chicks are safe and happy!