Some cats may need to be kept permanently indoors and this can work as long as owners are aware of the responsibility that it brings. For others, access to outdoors needs to be restricted, but owners would like to offer some contact with the world outside and in these cases, there are a number of alternatives. The harness and lead approach is certainly one, but the fact is that not all cats will learn to walk in this way. Introducing harnesses as early as possible will help and making a kitten accustomed to the lead will minimize resistance to its use as an adult.
If you have tried introducing your cat to the harness and you have been met with overwhelming resistance you may wish to consider the use of an outdoor enclosure. Since cats can climb, the pen will either need a roof to prevent escape or have the sides angled inward at the top to prevent climbing over.
There are a number of commercial cat cage containment products for both indoor and outdoor use. Ideally, the pen will be accessed from the house via a cat door flap and will offer the cat access to outdoors while offering you complete peace of mind. If an enclosure is to be used successfully it should mimic the outside world as closely as possible and cat furniture, tree trunks, toys, scratching posts and high up resting places should all be available within the pen. If the cat is allowed access to the outdoor pen when no one is home it is very important to ensure it is properly secure to prevent any chance of escape and the cat becoming lost.