Here's an option I haven't seen on the thread yet: One of my sisters allows her cats outside in harness, attached to a VERY long bungee cord (about 25 feet/ 7.5 meters). This allows them to explore the back yard, but not to leave it. (I think she also keeps an eye on them while they're having outside time.)

Aside from a life-imitates-cartoons event involving Misty chasing a squirrel, I think the kitties are quite happy with the arrangement.

Liz