Shading them won’t work. They will literally split or move to get back into the light (at least, in my experience, rhodactis and Discosoma will do this). I don’t believe rhodactis actually “stings,” but I think they are actually using some type of chemical warfare. I had a problem with rhodactis doing this to a large toadstool. Unfortunately I think the only solution would be trying to find a way to move one of the corals... the hammer may be easier, but eventually the mushrooms will grow into the next coral...