I put two strip of duct tape that are 6 layers thick and are about 1 inch wide by 2 inches long on the sides of my rollers for a rumble strip which alerts me that I'm about to start swearing if I don't start paying attention real soon.

Having an audible and sensual cue that I'm only 2 inches from the edge helps when you get to the point that you can watch tv. If I get too far off-center, I hear and feel a bububububububub sound that snaps me out of my daydream right quick.