The fasteners (3) engage recesses (4) on the rear side of the guide plank (2) to hold the lower part (1) in place. An inserting part (5) can be coupled to the foot part (6) of a marker (7) and is inserted onto the lower part, surrounding the top edge (8) of the guide plank.The lower and inserting parts form a releasable unit coupled to the guide plank. Pref. the lower part fasteners are protrusions, and the engaged recesses may be in the form of elongated holes. The coupling of the lower and inserting parts may be realised by coupling sections (9).
