What's the best/easiest way to make an aquarium divider? I'd buy one but I need it now and nowhere near here sells them.

I want to temporarily split a tank into 2 to separate some tiny newly morphed froglets from some larger froglets that finished morphing a few weeks ago. I'm separating them so that the larger ones don't try to eat the smaller ones. The two halves of the aquarium will be sharing a heater and a filter so the water will need to be able to pass through the divider. It will only be temporary so I don't want to silicone anything to the glass (plus I don't have time to wait for silicone to dry).

My plan so far is to use needlepoint canvas providing the holes are small enough, but I can't work out what would be the best way to secure it in place and make sure no little froglets can squeeze through the sides or underneath. Any ideas?

Thanks.