How do I get my cat to stop peeing on the rug?

I have 3 cats and my 4 year old Maine coon named Harlee keeps peeing on my rug in my dining room. She has always used the litter box until recently. I always keep the litter box clean so I dont know why she is peeing on the rug now... how do i get her to stop and how do I get rid of that smell???