@Purp, I used to keep my cat on a long cable and harness when he went outside. Sometimes he got stuck by wrapping himself around trees and such. Supervision is always good and if you cant do it one day, maybe they don¬ít get to go outside.
That's why I'm still exploring options. I've always kept them on leashes with supervision when outside. I originally wanted to put a cable up for them, but I have quite a few trees and obstructions in my yard.