The wikis look great but we would like to control who

The wikis look great but we would like to control who is able to look at them. We looked at the settings and the only thing that seems to be there is an ability to control who can edit. That does appear to be working.

The upper right there is a publish box with a visibility setting of "private" available. I set it to private and still the public can see the Wiki. What do I do to make the wiki only visible to staff for instance?