i think you should reduce the specularity of those rocks, we can even see the reflection of the lights that are behind the camera.
Concerning the rocks, as you appear to like realism, i would change the shape of the forth one, it would never stand that way. Remember that the center of mass should be above the supporting area, which is not the case here, it looks a bit unbalanced
Thanks for your comment. I got your point on the centre of mass of the whole object. I will surely modify it.