Any of you have an indoor/outdoor cat (or cats). How did you go about getting them used to the outside, so, that they didn't run away?

If one moved to a small apartment and wanted to have an indoor/outdoor cat (so, that the cat wouldn’t feel so cooped up in a tiny space), what could one do to make sure that they don’t wander?

This cat is already an indoor/outdoor cat. Just dealing with new surrounding now and want him to stay close to home.