The easy way…

Using long-handled pliers or, better yet, Vise-Grips, start at the rim of the pot and I crush” little areas at a time in the jaws of the pliers. With the Vise-Grips this should be an easy, but somewhat lengthy, process. It will be more difficult with the pliers, especially around the rim, where the clay is thickest. With the pliers, you may end up twisting off small chips instead of crushing them, which is a bit more dangerous, as the pots have an exasperating tendency to crack in unexpected directions. A third method is the “scoring and tapping” method, which uses a small sharp grinding wheel to score out a proposed fracture line along the pot, Cutting one-third of the way into the pot, then, using a small ball-peen hammer, gently tap on the inside of the pot along the scored line. The pot will usually break cleanly along that line. This technique works best along straight lines and is good for splitting pots lengthwise to make two long, low caves. For small curved openings, it is best to use a combination of these last two techniques - scoring the outline of the desired opening and then using the pliers to chip or crush it out. This really works quite well. No matter what technique is used, you should go over the broken, or chipped, edges carefully with a coarse rasp to remove the sharp projections and smooth the surfaces as much as possible. After all, you are trying to make
your fishes more comfortable, not harm them. If you are making shelters for a  community of aggressive fishes such as many of the African cichlids, you should cut a medium size “front door” in the pot and a small “back door” as well. This allows the smaller, pursued fish to dash in the front and duck out the back with its larger pursuer unable to follow.

To anchor the wood, set your decorative piece in a position that is most pleasing to your eyes and choose two inconspicuous spots on it where you can drill holes. If you can manage it, have the holes in the back where they won’t show. Don’t hurry drilling the wood. This is a work of art remember, and not just any old decoration.  If the wood is still wet, the drilling will go slowly, but don’t overheat the bit. The bit should be just large enough to allow your plastic tubing to slip through the hole it makes. Next, put the tubing through the holes and set the whole thing on the slate. Mark where the tubing hits the slate and drill matching holes in each end. Put the tubing through the slate and the wood, and trim off the excess. Heat the soldering iron and melt the plastic on each end of the tube into a flat disc - you’re actually making plastic nailheads. Make certain that everything is secured, then let everything set for a few minutes.
Put it in your tank and cover the slate with gravel. Now you have a beautiful piece of driftwood that will stay put.