Whenever my yellow sheets are on the bed and Lady is allowed on the bed, she whizzes, and always in the same spot. I've applied Nature's Miracle to the mattress cover, so we'll see how it works. Other times I'd just tried kennel cleaner and disinfectant. The only two times Fuzzball had ever whizzed on the bed were in that same spot, so I fear she may be picking up residual "essence of Fuzzball" from there. If that's the case, nothing much will help.
It also never fails that I notice Lady's "handiwork" just before I'm about to go to sleep. I'll kick my foot over, and eeeeuw.
I learned from dealing with Fuzzball and Monty (Mom's dog) that Bichon Frises have this tendency to be passive-aggressive and use "creative" whizzing and defecating to show their displeasure. This one, I think, doesn't like yellow.