Beat the marking and finish the routine. Lose your marker with a check and a burst, get across him at the back post, and finish the flick first time.
As the base, but a defender marks the back-post runner. Emphasise the runner's movement to lose the marker, a check away and a burst across to attack the flick. Start with the defender passive, then live. Rotate the roles.
Fork it into your private drills, then change the animation, adjust positions, swap equipment, or drop it into a session block.