Because we first brought Duke and Clemmy home to our Cedar Rapids, Iowa apartment, they became, by default, indoor cats. (Our apartment happened to have a "no pets allowed" policy, but as we only planned to stay in the complex for two more months before moving to Michigan, we took a risk. We also got caught, when both kittens started habitually sleeping and playing on the back of the couch in front of the window, and had to pay a hefty fine.)
During their two months in our Cedar Rapids apartment and almost a year in our Ann Arbor apartment, Duke and Clemmy had minimal exposure to the outdoors. When we finally moved into our first house and let them out in the backyard, they went CRAZY. Duke in particular behaved as if he'd gone rabid, hissing and howling and biting with a viciousness we'd never seen in him before.
After watching Duke's reaction, we decided it best to keep both cats indoors, but doing so only made them even more desperate to escape the confines of our (warm in the winter, cool in the summer, cozy, well-stocked with food and water and toys) home. Tom and I perfected the art of entering the house quickly, with one hand blocking the gap, and by the time Will and Hallie reached 18 months old they had both learned how to keep the cats inside as well. "Uh oh, Dukie no go", was one of Will's first full sentences.
Duke and Clemmy did periodically escape, usually when someone who hadn't yet become familiar with the block-and-enter technique came over. I had more luck than Tom "hunting" them down, so when they headed out into the neighborhood I had to don my heavy-duty grill mitts (as soon as he was outside, Duke couldn't recognize me and therefore treated me like an animal he wanted to kill or who wanted to kill him) and prepare for a 30+ minute adventure. It was during our Ann Arbor years that I earned the nickname "the cat whisperer".
To make a long story short…I know, too late…Tom and I decided long ago that when we brought our next cat home we would allow him/her to go outside from the very beginning.
Our boy LOVES leaves. He chases them. When he catches them, he sniffs and licks and sometimes eats them. He plays with and in them. He digs in them. He poops and pees in them. He traps and incapacitates and tries to eat lizards in them. Once Tux goes outside, leaves are his whole, big beautiful world.
Tux goes out and comes in all day long, which while slightly annoying to those of us humans who have to open and close the door all day long (I refuse to put in a cat door lest other animals use the door to gain entry into my house), makes him the happiest cat on the block.