He's A Bit of Close Talker

How do you deal with someone who is always in your personal space? They don't seem to get the hint when you step away, and more often than not, they corner you and while backing you up against a wall, also cut off your exit. I've even tried "boxing out" like I did when I played field hockey in high school. I'm considering getting some masking tape and marking off my personal space on the floor. Or maybe getting a hula hoop to carry around with me to provide some sort of barrier they actually run in to. I've tried being polite, and that doesn't seem to work, so I'm running out of ideas. Help!