I know your pain. When I moved in my current house ten years ago, my garden was the neighbourhood cat toilet. One of the close neighbours has around 15 cats, apparently they all have different personalities, he is a bit of a mentalist. I laid a new lawn, went on holiday for a fortnight, came home to a lawn covered in shit. It had burnt holes in the turf. I wanted to kill them all, but there were simply too many.
I tried many things, my own piss, pepper, bleach, jeyes fluid, water bottles, mirrors, throwing bricks at the bastards (put a hole through the fence). Nothing had any effect.
Then I errected a big shed in the garden and it stopped overnight. They all started shitting next door. And the poor neighbour could regularly be heard screaming, ‘facking cat shit!!!!’ So my advice, throw bricks at them so they know you mean business, then errect a big shed. Its what worked for me. Good luck.