All the above..
And, I've also taken a mushroom (or even lose polyps before), 2 small pieces of rock rubble. I place the mushroom foot between the rocks and rubberband the rocks together creating a snug fit on the foot. I don't rubberband it so tight that it is crushing the foot...just more of a way to keep it stabilized while it attaches.
I use Jims idea, I take a shallow box put rubble rock in there and put a small screen on top, still gets enough flow on top of my Frag rack but they can't come out. After a few days they attach. I also stick small zoa polyps in there as well if a few come loose from somewhere. Turns out some nice little rubble frags