you might want to use some netting to help hold down the mushroom till it ataches itself to the rock, I've tried using super glue gel to glue newly fragged shrooms to a rock before and it only works 5% of the time, the problem is that shrooms like to secreate (I know I didn't spell that right, i think) alot of slime and it makes them hard to attach with glue.
Rubble is a another good way, as suggested above