depending on what you need the divider to do, you could possibly use a net (or mesh) of some sort that's held at the corners by suction cups. Or you could use plastic sheeting (similar to a really thin cutting board) that you can buy @ Walmart (arts & crafts section).. if you're talking about a long term solution, i don't know if there are dedicated dividers that big (i'm sure there are, but it's a matter of finding them).
You know crayfish can climb the net/mesh right?
In honesty, I hate dividing a tank. I'm keeping some land creatures right now and sometimes it can become a pill.
I think what you need is a little visit to both your LPS and home depot. Home depot carries stuff that you can use as a divider. Since crayfish can't climb smooth surfaces like plastic and glass and they're not so small as to being able to fit into teeny tiny cracks/openings(babies I'm not sure) you can go in there and look for maybe for plastic sheets or glass and fasten it in place with something cheap like plastic suction cups. However, I tried doing this and boy was it expensive.
Another method I tried was finding a large rectangular glass and going home and using a glass cutter to cut it but that didn't work out too well either cause I admit, I'm not very handy
Don't even try asking for advice. I went up there today and I asked one of the workers [edited] I look for the item code on the shoplights and asked one of their workers if its the same one just because I'm paranoid. He comes and looks and he's like, no that's not it.
So I'm like, but it has the same item code, has dual/double light strips, also uses T10 bulbs, and is the same size and everything, are you sure?
He's like, yeah. Then I said, okay, if this is not the same item, can you show me which one it is, referring to the models they had up for show. So he looks around cluelessly. Then I put the lights that I was holding for what I thought was the item that I wanted that was in the box and I said, see it even fits.
Then he's like, I guess that is it, hrm. Have a nice day, and walks away.
What happen to quality workers instead of quantity? I once asked a worker in there where the duct tape was located and he pointed me to the other side of the store and later found out that we were standing in the isle that had it the whole time. I can't call him blind cause I'm no better but
Sorry for getting sidetracked on your thread.
Well, what I'm doing currently is. I eventually went to the arts store and got some mesh. I know crayfish can climb it but so can my creatures that I have now. But this is what I did. If you're not against some hanging on to the mesh, but concerned about them climbing over the division or out of the tank then do this. For the top part of the mesh, stick some smooth plastic sheets (from plastic containers like salad containers) or whatever you find. This way they can't climb past the top part.
This idea needs revision but it did the trick for me. I'm not the best handyman but at least I got it done and cheap.
I'll leave someone else to give you better advice. I wish we had force fields invented, so many uses.