indoor cats
Yep, indoor cats live 15-18 years, outdoor 3-5. Disease, injury, predators (there are hawks, foxes and coyotes even in the city), cars, dogs, other cats, and rotten little kids with baseball bats, not to mention the low-lives who steal cats and use them as bait to be ripped apart to train fighting dogs, or sold to labs for dissection or experimentation (they love the friendly ones)--those are the hazards facing outdoor kitties.
If you're ever in a position where you have a yard or can build something, like the cat fence-in idea, that's perfect. There are many other kinds of cat enclosures, from the small and simple, to a huge cat Disneyland; we profiled a couple of these in our newsletters in October and November (
http://www.littlebigcat.com/index.php?action=nlarchive).
If he's never been outside, he doesn't even know that world exists. As long as your cat has a sunny window, scratching post, toys, and plenty of attention from *you*, he will be perfectly happy inside.
Cheers,
Dr. Jean