We've had instances due to injury that we could not let each of our cats roam as they would. A harness and leash were the only options. Each of them responded differently to the situation, of course, but all were ultimately happy in the end that we could take them out for supervised kitty time.I think I'll have to get a cat leash and give it a try. Worst that happens is that neither cat takes to it, but a walk outside would be fun.
The hardest part was really identifying where they would want to go potty since they all categorically refuse the litter box. My favorite is Iggy who will quite gladly use a gopher mound!, and around here, those are quite readily available.
On the flipside... Beware trees. There is absolutely nothing worse than a cat on a leash deciding that the tree might be their path to freedom from their opposable-thumbed oppressors.