There are lots of different versions of tank dividers that we use. Much of it depends on the size of the stomatopods, how the tank is plumbed and it size, and how much you are concerned with aesthetics. I like to maintain maximum circulation and current, so for O. scyllarus in tanks over 40 gal we use egg crate dividers The O. s usually can break through them, so tie a piece of plexiglass strip (usually 3 or 4 inches high to to the bottom. This provides maximum flow and allows them to interact which I feel stimulates them and keeps them active.
For smaller animals in smaller tanks we use plexi with 3/16th inch holes drilled in a grid pattern every 3/4". (That is a lot of drilling!). I also have some pressed polypropylene chip material that was used by Instant Ocean for their sub-gravel filters. Great stuff and very porous, but I can't find it anymore, so I guard what I have. If anyone knows what I'm talking about and has a source, please let me know.
Make sure that your intake and outflow are on opposite sides of the partition and I usually install at least two powerheads, one in each side.
Roy