It is not mandatory to mark the ball.
As the ball (seemingly) was not actually on the rake then he should have simply removed the rake.
If that causes the ball to move it must be replaced (not dropped). 24-1a
If it was in fact on the rake, the ball should have been lifted and the rake removed. The ball must be placed (not dropped) on the spot immediately under where it lay. 24-1b
In both cases, if it won't come to rest it must be placed on the nearest spot where it can be placed at rest not nearer the hole. 20-3d(i)
Loss of hole for a breach of rule 24.