We keep our cats inside the house. The older one may remember how we rescued her years ago from a rain storm. She has no inclination to go outside. But the younger one spent more of his life as an outdoor feral cat. Though he was quite seriously damaged numerous times in fights with some other animal, he still longs for the free air and the adventure of the outer world. He has managed to escape the house briefly several times but was quickly captured and returned to "his prison." We nicknamed him "the escape artist." While he seems to have finally adapted to his confinement, I still occasionally find him sitting in a beam of sunlight, staring seemingly morosely at that exciting life outside the glass door.
I have thought of getting one of those cat harnesses and leashes but I suspect Blackwell would react to it like this cat did.
It's not easy, being the companion of an indoor cat.