Perspex. Am thinking of creating some mini terraces and possibly plant containment - e.g. raised terrace full of pygmy chain sword, so I can let it go mad in one area and not worry about keeping it out of the rest. If I get around to it I'll probably just cut 1 mm oversize and jam it in - but I can do nicer shapes if I glue it
Get some Perspex or glass and make rectangular planters for the chain sword. Basically make small glass or Perspex aquariums about 6-12 inches long x 3-4 inches wide x 3-4 inches high and fill them with gravel and put the plants in that. Spread a thin layer of silicon on one side and sprinkle gravel or sand on it or stick thin rocks or driftwood to it so it conceals the glass/ perspex.
You can also use small plastic icecream or any sort of food safe plastic containers for the plants. Spread a thin layer of silicon on the outside of the container and put sand, gravel, rocks or wood on it to camouflage it.
Get a square or rectangular piece of Perspex about 6-10mm thick and glue the rocks/ terraces to that and put the entire piece into the tank. Then you can move it out afterwards.