Deterring Cats from Scratching Furniture - HELP!

I'm looking for YOUR suggestions again, because my kitties are driving me bonkers! I have a new couch, chair and office chair. (Hurray especially on the office chair! My old one was so sad and rickety, you would've laughed to see it.)

The couch and chair we've had for around a year, and already we've had to drape blankets on it to prevent our two cats (especially one is guilty as charged, the little monkey) from scratching. I've tried a few natural ideas I've seen posted on the Internet - like spraying the area with lavender. But I think my cats (like me, apparently) love lavender! It didn't help a bit!

Is there any other way to prevent them from scratching up furniture? They DO have a scratching post...I've heard that orange oil might work. Has anyone tried this?

Thanks all!
Christina