Motion sensor sprinklers,chicken wire in garden beds plants will grow up thu them Please don't use anything that will burn them Cayenne pepper,peppermint oil etc. it's down right cruel causes severe burns & injury to nose mouth eyes.
Put some dog hair around the scrubs.....they font like cinnamon either
If you don't have an outside cat, place citrus peels around the perimeter. Cats hate that smell and should leave.
Spray Ruta Graveolens essential oil around your yard, porch areas, walkways, etc. Cats hate the smell. You can also grow the plants.
Cats dislike heavy plantings of lavender and rosemary, but cayenne pepper and essential oils of orange, peppermint, and orange peels also deter them.
Since they're strays, consider calling animal control to pick them up. The reproduction rate, spraying habits and defecations can be quite disturbing, and they can carry diseases you don't need.
Plant Catnip in your Neighbors Yard.