Frustration = H2O?

I am becoming increasingly frustrated with Katie's constant scratching on my couch and recliner chair. Sometimes I will remove her from the couch 3 or 4 times in a row. Each time I remove her I give her a stern "no" and put her off the couch. 2 seconds later she is back scratching again and again and again. My roomate is amazed at her inability to learn. I've researched online as to how to train her to use the scratching post (play around the post, etc) but it doesn't work. Someone else told me that using a squirt gun as negative reinforcement works. Guess I'll try that. : (