We have no fence and face a pretty large greenbelt that leads into the Cascades. Makes for unbelievable scenery, but it also brings with it quite a few bears, bobcats and coyotes, which means literally zero worries of neighbor cats (or for that matter, small yappy dogs). I like cats though.
Our two are indoor only, luckily for the hares and birds but unfortunately for their sometimes bored selves... But I've had to chase coyotes out of the backyard with a pitchfork. They just aren't afraid and will stare you down like, "You mad, bro?" or sis, in this case.
The bears are amazingly strong - they rolled/dragged this thing a full 150 feet uphill, making it entirely unfeasible outside of an electric fence.
http://www.amazon.com/gp/product/B00008Z9ZF . It was shoddily built anyhow. Me = dupe.