Covers Securing the top?

The way my projects usually go, I get started, think all's going just peachy, realize I have made some massive and incredibly stupid error, find some way to fix said error, and then I usually end up happy with the result. Well that's the story of the second C&C cage I've made which I just finished. (I use that word loosely!)

When I made it, I was thinking I'd make the top removeable and that way the bottom would be really easy to clean. So I finished the top and then realized uh... so how am I supposed to secure this thing? I was thinking of using some thick ribbon or fabric strips and I'd just untie it whenever I needed to clean the bottom, but that seems like a bit of a pain too. Any ideas? I'm just looking for something that will hold the top level on tightly, that can be easilly removed but without compromising safety. I made the top level slightly larger than the bottom level and there is some support on the bottom, but the whole mess it just a little flimsier than I'd like. Unable to post pics right now because I still haven't found that camera...