I'm not a big fan of the rubber band method either, because it constricts the base too much (until the point where it can grow around the rubber band, it will stay closed). Better to peirce it with a toothpick or a needle and fishline, and attach that to the rock.
Sometimes I just tuck it into a hole, and it will attach within a day. The problem is that if it gets unattached that first day, it can get blown around the tank and go where it wants (which is usually where you don't want it to go)
One technique I've been using lately is I just rip the stuff off the rock, and I put it in a large jar which sits in the middle of the tank, and shares circulation with it. I put some rubble rock or shells on the bottom. Within a day or two, the little stalks will have attached to rock, and can be moved where they are most attractive. If the rocks cannot be tucked where you want them to stay, you can attach them with 2-part plumber's epoxy (glues do not work on the stalks themselves, though, since they are soft and have a slime layer).