The water hazards at TPC Sawgrass have wooden retaining walls which I would think would be covered by the definition of “immovable obstruction”. In the recent Players Championship, It appeared that if a player’s ball came to rest outside of the water hazard but the player’s stance was on or interfered by the retaining wall, the player apparently was not entitled to free relief from the wall and had to play the ball as it lay. The only reason I could see that there was no relief available is that there was a Local Rule making the retaining walls “integral parts of the course”. Does anyone know whether this is the case?

Artificial walls are integral parts of the course when they are located inside a water hazard.

(USPGA “Hard Card”, the permanent Local Rules for all USPGA tournaments)