On the LHS of the drill there can be seen two red levers.
Attachment 424430
The lower lever locks the head in place on the column. The upper lever locks the built-in depth stop where you set it. Both work well.
One disconcerting aspect of my drill is that, as you rack the head down, the locking position does not move with it until the head gets close, then, with a loud bang, it jumps down to a new position. Scares the hell out of me every time.
I have not found much use for the workpiece holdfast. It seems pretty clunky to me and I prefer to use a drill press vise instead.