+ to the plastic mesh... I got some gray one and used the window frame kit from Rona... Best investment ever and it fits perfectly over my tank... I would have lost many fish by now if it wasn't for the screen.

I'd love to try the clear stuff and might order some from BRS one day.

I saw clear mesh (about 1/4" squares) at Canadian Tire yesterday. It's in the gardening section as "bird netting"