Very cute story.
I'd first try mesh minimum of 12 inches hight w/velcro. If that does not work you can always go with a babygate that is more dense.
Here is a link to same babgate I use for Rocky & Daisy:
http://www.burlingtoncoatfactory.com...rchedProduct=t
Cost is only $12.95 and they always seem to keep stock of these in the store.
I use these in the laundry room where they sleep. This way they never have to feel they are behind closed doors.