Here is a couple ideas
Dogs! Just kidding(kinda). Try this: https://amzn.to/36VFN4W
Cats are good climbers a fence won't help.
Use garlic water and spray around where you know the cat comes in
motion sensor sprinkler
Use scent to keep the cats away
Pepe...l suggest you talk to the owners...hope you know who they are
Hi Pepe. Spritz lemon juice where they like to go. A large bottle of lemon juice is an inexpensive and effective way to keep cats, and other animals, off your property.
I've seen people say they used video tape around the garden which, presumably, frightens the cats away as they think it's water.
You can buy big cat rocks from your local pet stores, and these are from zoo's. The household cats smell it, and think a huge thing like a lion or puma is around, and they go away. (Not tested by me).
Cats have very keen senses of small and taste, and commercial repellents are available to discourage unwanted cats. Natural repellents to sprinkle on flowerbeds or gardens include moth balls, ammonia soaked rags, ground mustard, cayenne pepper, citrus peels, coffee grounds, and citrus-based sprays.
The best way is to have a cat of your own, they will defend their territory, or buy in some large Cat dung and spread that about. Could be available for Zoo! There are other ways but none are very good as cats are clever animals and has minds of their own. Sorry I can't be more positive. Unless you add very high fence or railings......
A motion sensor sprinkler/sprayer, it activates as the cat approaches sending out a stream or spray of water and they hate to be wet. This will also water your lawn or garden, wherever they happen to be visiting you. You can find these at diy stores.
Here's a post that might help you - https://davidsuzuki.org/queen-of-green/keep-cats-garden/