How do I get my Shih Tzu to stop pawing at the door when I leave?

My Shih Tzu is going on seven years old. She absolutely loves to be with me, but most times when I leave the house to go to work or just to take the trash out she is steadily pawing at the door wanting out. I've tried catching her in the act and scold her but she just doesn't care. I've gotten to where when I leave the house I put her back in my bed and she rarely jumps down, but this isn't going to fix the problem. Besides this one behavioral issue, she is the perfect pet. I'm afraid one day she'll hurt herself and want to correct the problem. Any suggestions would be greatly appreciated! Thanks!