It also takes patience and a lot of tolerance, but you can turn an outdoor cat into an indoor cat. My two now have never been outdoor cats, but I had an old boy who was. When he was getting old and really very much unable to defend himself - blind in one eye, arthritic... I started keeping him in. He didn't very much like it for a while. There were bouts of seemingly endless meowing at the door... but he became accustomed to it relatively quickly and he became happy with his situation.