Easy solution - have two litter boxes.

                 -MIKE

There must be more to it, though. The cats have made their mark a few
times on a bed in my house that has never seen sex. Was the bed made?
This bed is very small with an extra large quilt that's always
wrinkled and folded all over the bed and when they have urinated, they
have tried to "bury" it like in the litterbox. After it happened, I
put a waterproof cover on the mattress because I was afraid the scent
would draw someone back to it. So now when it happens (and
occasionally it still does), it doesn't soak into anything. It's as
easy as throwing the sheet or quilt into the washer.