Possible Clues:

• Planking for marshy ground
• Bird table that sits on a path?
• A wooden walkway over swampy ground
• Dodge bloke carrying extremely angular wooden slat
• Wooden aid for walking over wet ground
• Dear directors, this should keep you out of the mire
• How to tell the directors to keep their heads down when they've got this underfoot
• Tell the directors to keep their heads down under their feet
• Advice to the directors to get their heads down or they'll get underfoot
• Bob oversees directors? That'll keep them out of the mire!