In my experience, physical barriers work better than chemical repellents. Cat "scat mats" have pointy protrusions that cats will not walk on. There are motion-sensors that spray water or emit a high-pitched sound when motion is detected. If I were you, I would plant a catnip patch to attract them--and keep them in that one little area, away from the rest of your flower beds. If all else fails, you could find out from your municipality what the laws are regarding wandering pets, and start a dialog with your neighbors.