How do I get my cat to stop scratching something it shouldn't be?

My cat keeps scratching the carpet near mine and my roommates' doors (so it can get its paws under the door and ultimately attempt to pull it open). I have tried ignoring it, but it does NOT quit- it will go for 20 minutes if you let it. I have tried verbally reprimanding it or banging on the door when it does. I have even squirted it with water a few times, but now it just stands back when it hears me get up. Is there something that will deter the cat?