The best way to cement the DIY plastic canvas dividers is to get the bindings for report covers, then seal them to the sides of the aquarium with aquarium sealant.
Then cut the canvas to size and slide it in! It'll stay forever pretty much! :D
Here's a couple of shots of my DIY dividers:


Sorry the side shot is so big, I thought I re-sized them. As you can see, report cover, cut to fit, glued to sides. Sometimes if you're not careful they'll go crooked, as you can see. If the tank is tall, you can glue one in, then cut another to fit the top half.