Another trick is, in chaotic handheld tracking shots, to light up the set and stop the lens down for a large depth of field. If you watch the long scenes in Children of Men for instance, even objects far away are sharp; this is because lens is stopped down. That way the subjects stay in focus even if the blocking is not terribly precise. In those long shots, Cuaron uses framing and contrast to direct your eye, rather than focus pulls. He creates depth with haze, which reduces contrast in distant objects.