[You can put it where you like it, affixing it with a rubberband gently. Or you can wrap that rock with some bridal veil / netting for 5 days. Or you can pin it in place with a toothpick like Amanda did recently.]
[LOL! You should stick it through the mouth, not part of the body. You also need to stick a wad of epoxy to the top of the plastic toothpick to keep the shroom from coming off. I prefer this method over the others and it should attach fairly quick.
[Thanks for the help. Looks like it's for the most part attached. I'm avoiding that area of the tank with my cleaning magnet for a few more days so that it is attached strongly, but it's not drifting anymore.