Edit: Golf Show video no longer available. Replaced with this one from GolfCanada.
Ossie Moore took viewers through an important rule concerning immovable obstructions, that I’m guessing many golfers aren’t aware of.
If your ball comes to rest near an immovable obstruction, such as a tree stake, sprinkler head or cart path, you may take relief without penalty – drop at the nearest point of relief, no nearer the hole. It is worth noting that you can only take relief if your swing or stance is obstructed or if the ball lies on the obstruction. You do not get relief if the obstruction is merely in your line of play.
The video below courtesy of The Golf Show talks a little more about a situation where free relief is mandatory. In this case, relief must be taken because of the local rule concerning staked trees.