update:

I tried the dryer sheets. He sniffed around it and left (the only problem is it's so stinky *I* want to leave the couch! I had to take them off while I was sitting on it). I also moved the cat bed onto a nearby cupboard so there should be nothing to attract him on the sofa. I also put sheets of aluminum foil - he ran away when I was tearing them out of the box.

It doesn't look like anybody was on the couch overnight as none of the sheets were disturbed. It's not pretty, but better than having a tattered sofa. Let's hope it works in the long term!!