Locking lid?

How can I make a locking lid for a terrarium I have (50 gallon, splitting it off to with a cage divider). So I really don't want that to go to waste.
So anybody know how to make one? That would be great. To list like materials, and how to do that stuff. You know. :P

Can't imagine what kind of terrarium that is so maybe a picture would be nice. How does it open?
At first we used regular duckt tape to securely lock the sliding doors now we use a lock:

http://www.pickardhardware.com/image...-%20CF4100.jpg

Hope this helps ;)

Go get some hardware cloth and some wood trim. Measure the wood trim and cut to the size you need. You can make it a split top so you can only open 1/2 at a time. Use a regular lock on front and back and vala theres a split locking top that is secure. You will have to experiment with it a bit at first. Just make sure its very snug when on the tank.