Thanks for all the great ideas! Abby and Bo stay inside too, but they don't seem to mind. They're both older - Abby has always been an indoor cat, but when I lived in the country Bo was allowed out (he was a great hunter). Since I live in town now I keep them in. The other two seem perfectly content and never run towards the door, or look so longingly at me to be let out.

I did get the harness on her and took her out for a little bit this afternoon, all was fine until some idiot in the neighborhood set off a firecracker. She got agitated so I brought her back inside.

I'll look at Petsmart and see what I can find, thanks!