There are various repellents you can use,but it is temp and costly in the long run.Best bet is to live trap and take in to the pound.You can rent a trap from animal control.
If you think the owner(if you know them) is receptive then consider talking to them about the problem,and suggesting they build a cat run. A few fines will get them to reconsider if they refuse to keep their pet in their own yard.Cat urine lingers and cats have a habit of peeing around a house foundation. Very nasty.
If there is one spot that is a toilet you can lay some foil or chicken wire,but they will move to another spot,and another....and so on.
Less frustrating to just remove them from the yard than try to repel them all the time.Cat enclosures are a wonderful option for cat owners.