I'd go
1) repellant from hardware
2) some councils or animal shelters can (for a fee) trap them
3) ratsak in food. Is a permanent solution but raises ethical issues.
Best plan of attack is to borrow a cat trap "steel cage" they are legal at least in SA they are, whack a bit of meat in it when you catch the cat you call the dog catcher "council animal controller" and they take them for the big walk.....had same problem here 26 cats later the problem subsided, if council doesn,t help once you have caught it refer back to post 19. Removal is the ONLY answer repellants and such don't work. if you have a slug gun and lots of time (a bit crueller) but it is workable, but you must not let the cat see you they have to think the sting of the slug is associated with the yard not you that way they will avoid the yard and not you. believe me both these ways do work although the slug gun approach is a bit radical.
Yeah mate pepper works my mum used to put it around her car so they wouldnt jump on her car at night, she also left a bit of brandy in a bowl for them and they never came back, I think they couldnt find there way back, haha thats not a joke man im being serious, pepper and brandy