just like sturner stated. Dollop of SG gelk on patted dry rubble on the shrooms stem, place on rock inside tank and hold for a second or two. Its best to make sure there is no loose debri on the spot you want to attach the piece to as well, as you will only be glueing to loose substrate then, which will not hold long. Shrooms IMHO are best placed with apin to hold them inplace for a week or so. Remove as much substrate or rubble from the shroom itself. Place shroom in place, insert a pin or needle through it near but not through the mouth. Cut a piece of rubber band about 1/4" long and stick it over pin first, then stick shroom. Once pin is pushed and wiggled into live rock, and its holding, slip / slide rubber band piece down to hold shroom against live rock firmly. Within a week it will adhere to rock naturally. Then just wiggle pin and pull it out and your done. No unsigntly nets or stings etc to deal with and it does not hurt shrooms or other corals at all, It works fine for leathers and polyps of all kinds. Live rock is relatively soft anyhow so getting a pin to hold in it is pretty easy. The closer you can stick pin to the mouth or on an angle near the mouth so it exits out the stem the better and quicker the shroom will adhere in place.