As of this very moment, all three gerbils are back in the cage!
How to keep three gerbils in the cage......
First, you catch all of them in various places in the house, during various days of the week, in various times of the day/night.
You place all of the gerbils back in the cage.
Then you grab the kitchen mat and place it on the cage as quickly as possible.
Once the mat is in place, you get all of the Reader's Digests that you own, and place them on all four corners of the mat.
Once completed, you laugh the evil laugh, do the victory dance, and bask on the goodness that all is in the proper place.
You go the more productive and better looking route and go to Petsmart and buy a screen to put on top of the cage.