Thanks so much for the ideas.
I didn't have time to go out yesterday and buy anything though. I wanted something for last night and in looking desperately around the house I found some velcro. It is sticky on one side and velcro on the other. I didn't have enough to do 4 sides but I am going to pick up some more.
I am also going to a reptile show this weekend and I will see what one of those locking tops goes for but $ is tight right now.