You can use predator urine to repel them. But you should really contact your local animal control department.
I would use bleach to down items like a porch. That would just be to get rid of cat scents. Sprinkle cayenne pepper around the yard.
You can buy red or black pepper (as in, a 2 lb container) and liberally apply it around where you see the cats--but it also can cause a problem of your dog/child gets into it.
Another thing is citrus peels--get a load of lemons/limes and squirt the juice on shrubs, walls, etc., then put the peels around where the cats go--they absolutely hate citrus.
And if you could (I know it sounds weird) get some ginger root, peel it and put it in with the peels--it will make them gag and run like nobody's business. They hate the smell.
Make sure you don't have any spots around your home that they might see as a nesting area--underneath a deck, shed, etc.
Make sure none of your neighbors are setting out food for the cats--that could be why they prefer the area.
Get a have-a heart trap and capture the cat. Take him/her to a no-kill rescue center. They will neuter and if not adoptable, they will foster until he/she is or they will provide a home at their center. Do not scare the cat away as it will just go somewhere else without a home and have kittens and add to the feral community. Some centers neuter and release back to where they were found.
Sorry but I feed them and have them neutered and spayed as I catch them.
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