You should think about an enclosure. They can be simple and serve their purpose. You can have access to them from a window or door, then the cats can come and go as they please while still be safe (yet outside) and not an annoyance to the neighborhood.
There are a variety of kits available like this one:
http://www.catsondeck.com/?gclid=COb...FQyk4AodzgEAhg
Or you could build your own, as shown in a bunch of different examples from basic to extravagant here:
http://www.catsofaustralia.com/cat-enclosures.htm