Please provide some suggestions, along with web links, to some
authorative way to keep cats off a couch. Is there a material they do
not like? Is there a non-harmful chemical spray that can be applied to
a fabric on a couch? Is there a way to apply something to the couch to
keep them off of it. I try to keep cats off our couch, but aside from
keeping them in room, they wind up on the couch

Sticky Paws is an excellent product. You can place it on fabric, and
cats soon learn that they don't like the feeling of walking or
scratching there. Once the cat has learned to avoid the area, you can
remove the Sticky Paws, and the cat's avoidance habit typically
continues. It does not harm the cat in any way, and (unlike some
repellant sprays) it doesn't smell bad.

http://www.stickypaws.com/faqs.cfm

"Four Paws Keep Off Indoor and Outdoor Dog and Cat Repellent" seems to
work well up to 24 hours, after a couple days they get the idea.