A friend of mine lives in a neighborhood where there are many cats. So they needlessly "do their business" in her yard. She doesn't mind picking up a few poos in her yard every now and then..

But when it gets to spring cleaning, and she has to clean under her patio, she gets sick from the smell. That seems to be the hit place for cats do do their thing.

Is there anything she can to keep the cats out from under her patio?

Thanks