I'm still curious if anyone has found a way for their moss wall to stand flush against the back wall of the tank, rather than it sticking outward (like with suction cups).
I'd love to do a moss wall in my 5 gallon but my betta has a way of getting everywhere, even though she's blind. ie. Two different times when I removed the filter outtake so that I could fix the filter not flowing, she swam into the hole (about her size) out of the whole tank. Found her each time in the little compartment where the filter would go, even though I hadn't opened the hole for long. (The second time I wasn't done so when I fished her out, I had to plug up the hole with my finger while I worked because she was like "This is new territory, must explore again, is mine."
Last thing I want is for her to get stuck behind a moss wall, so if I can cut the right size mesh to fit the width and height of the tank, and make sure it's flush against the back wall, I'd feel a lot better. I don't think superglue would be a good idea, and suction cups make too much space between the moss wall and aquarium wall.