I like the canvas stuff a bunch! It's so easy to use and you can cut out the shapes you need.

My little sister (who lives up north with mom) used tinfoil to close up the gap in her aquatic turtles enclosure and wouldn't you know but that little fellow burst through like a circus act? She was very lucky that he didn't hurt himself in the fall! She's since begun to use the plastic canvas secured in place very well!