Sorry. I never want to assume on experience. I have a plastic food container that I drilled a bunch of holes into. This allows water to move through it. Then I filled with rubble (not sand) and small pieces of rock. Put the mushroom in this in a low flow area of the tank. Eventually it will attach to a rock.
Then you can take the rock and glue to where you want it in the tank.
Sometimes they do move when unhappy. It can be a pain because they get swept away and go wherever the current takes them. Into the powerhead sometimes. I have lost many a mushroom to somewhere in the rocks.