to mark off, you move it back to just outside the goal line. You're right, at some point, the distance has to be changed, but in those cases where you're inside the 10 or the 5, penalize as much as possible - don't move it back to the 4.5 if you're on the 9 on a 10 yard penalty - penalize them as much as you can as the yards on the penalty allow. Doesn't seem like rocket science to me.