There are many different types of coral and many different ways to propagate them. It's much easier fragging a stony coral, like an Acorpora, and just gluing it down with Super Glue Gel. Soft corals can be much more difficult but it gets easier to attach these once you get the hang of it.
This thread is about corals in the "leather" category. This includes corals like, Toadstools, Devil's Hand Leathers, Finger Leathers, Colt Corals, etc. The best way I have found to frag these is with a very sharp razor but sharp scissors can be used but puts more pressure on the coral resulting in a less clean cut. First of all, remove the coral from the tank if possible. This prevents toxins from the coral getting into the water column and affecting other corals. Then choose the area of the coral that you would like to frag and gently (and carefully not to slice your own hand) slice the piece that you have chosen to frag. It doesn't hurt to give both the frag and the mother colony a dip in a coral treatment or Iodine solution like Lugol's or Coral Rx and can help healing the cut areas more quickly. I've also found that it doesn't matter which part of the coral you choose as a frag. Example, you can cut a piece of a Toadstool's foot and grow a new coral from that just the same as you can cut a piece of it's head and get the same results. Once you have your frag (or frags) it's time to attach them to something so they can begin to regrow.
It's easiest for me to do it on a frag plug with a rubberband but rock in place of frag plugs will work also. Superglue will not work at all on these corals. They slime themselves off the superglue. There's no way superglue or epoxy would work. The trick is to keep them as still as possible and the rubberband has to be just right or the coral will come loose or split in two. I like to do mine on frag plugs so I can set them on a rack or place them on the sandbed and they won't move around too much. This can take a week, a month, or longer depending on light, water chemistry and how much the frag is disturbed. Hermit crabs, snails and other pesky tank mates can be a pain also when trying to give these corals time to attach so the more you can isolate them the better. I've never had luck with using fishing line to sew the coral to a surface and I've also never had luck with the toothpick method were you stab the coral with a plastic toothpick and then glue or rubberband the toothpick to a surface. The coral almost always ends up splitting in half when I've tried these methods.
Here's a pic of how I did mine. This is an example of a Green Sinularia and a Toadstool. A small branch was cut from the Sinularia and a small clipping was cut from the foot of a Toadstool.
Here is a pic of the mother colonies that were fragged.
I wrap the excess rubberband around the peg on the bottom of the frag plug and that's how I adjust the tension on the coral. If the coral is starting to get away then just slip it back under the rubberband and tighten it a bit. Look underneath the rubberband and make sure it's not too tight and cutting the coral in half. Just enough pressure to hold the frag still. Some pressure is good and the coral will start to grow around the rubberband and look like it's going to make two branches but don't worry about that. Just make sure it's not cutting it completely in half.
and the finished product.
Don't try to rubberband it facing up like it normally would grow. Just lay it flat on the plug and once it attaches it will grow upwards toward the light and right itself again. Get the most surface area of the coral you can on the area you are mounting it to. It will look sad at first but it will take care of itself and once it's grown a little you won't even be able to tell.
If you don't like the look of frag plugs then once the coral is firmly attached then use a pair of cutters to snip off the excess plug from around the coral and superglue it where ever you like. If it still looks unnatural just give it a little time and the coral should soon grow over the remaining plug and you won't even know it's there. You can also use reef safe epoxy to mount the plug to the rock work in your tank if you like.
Another method that was suggested to me but I haven't tried is using a jigger glass. Get a small glass about the same diameter as your frag plug, (like a shot glass) and drop the plug in the bottom. Place the frag on top of the plug and set the whole set up in the tank. This method might be good for harder to attach soft corals like Xenia.
If anyone has other methods of fragging and attaching these corals please post them here! There's always more than one way to skin a cat.