How do you play through full-pitch man marking?

If every player is marked, the space is not. I would begin with movement that takes an opponent somewhere they do not want to go. One player moves away from the ball, another uses the space created, and the player in possession can carry if nobody steps out. A useful practice is 4v4 plus three support players, with defenders asked to stay close to an opponent. The attacking team scores by finding the third player or carrying through a line. Do not solve it with constant rotations. Give the players one question: what space appears when your marker follows you? At U12, carrying the ball is often the first answer because a strict marker may stay with their player and leave the ball carrier free. The goal is to make the opposition choose between following the player and protecting the space. Start with a 3v3 directional game and give the player in possession permission to dribble through a line if nobody presses. That immediately shows the off-ball players why dragging a marker away matters. Once movement begins to create space, add the support players and let the group find the third-player option.