Keeping Cat From Peeing on New Couch?

I have a cat. She is about 4 years old. A few months after we got her, she peed on my bed once. She also peed on my sister's bed once, on the master bedroom bed once, and on the couch only once. It seems like she's peeing to "mark her territory". My problem is that we just bought a new couch. I'm worried she is going to "mark her territory" on it. Any advice? Thanks!

By Laureta