Tip boiling water over the rock if it’s new. NEVER boil a rock as it could explode.
Now take the plant and position it on the rock. Pay attention, remember the aim is for the plant to cling on to the rock so try to place it near a corner or ridge. Once you have the plant positioned secure it with a elastic band. You can purchase wire especially made for this or use cotton. However an elastic band it quick, cheap and easy.