button polyp

as some of you may know I am strong believer in "live and let live" (in most cases) and though it has not gotten to point where I am about to rip hair of my cranium, my button polyps are one of the most proliferate corals I have.

now, a while back (well over a year ago) I re-aquascaped my system and I wedged a rock "up side down" this rock had a small colony of polyps on it that finding themselves suddenly without a direct source of light started shrivelling away, though they persist to this day.

iv noticed this with other colonies shaded by a plating coral for example. I was wondering how feasible you folks think it is to control polyps simple by "starving them" from light? and what material would you use if you had to do so?

or if you have any simpler means of control....

P.s haven't thoroughly researched the latter....