The General Committee has decreed previously that the rakes should be in the bunkers.
After use, the rake should be placed into the middle of the bunker, parallel with the fairway and the green.
The most important thing is for the rake to placed away from the edges of the bunker, as the ball can be held there by the rake and sometimes unplayable.
There are many thoughts on the placement of the rake. One good reason for the rake to be in the bunker is that if left outside of the bunker, a good shot can then be deflected into the bunker by the rake. Whereas it is not usually a good shot if the ball gets into the bunker on its own.