Block/charge and line

[so cal lurker]

NFHS legal guarding position. If a defender has a foot on the baseline (or sideline) can he have legal guarding position to take a charge, or does it automatically become a block? And in the real world, how tightly is that monitored -- do you call it as closely as a player with the ball being out of bounds? And last, is my memory correct that this changed a few years back and it used to be that a defender could set up with a foot on the line to ensure it was impossible for the dribbler to go around?