If your cat wants to go outside, it can be nearly impossible to convince him that it's not safe. If you have a fenced-in garden, you can build your own cat-proof fence to keep him confined to the safety of your property, allowing him some of the freedom he wants. In return, you will know he's a lot safer than if he were wandering freely among dogs, other cats, the wrong kind of people, and cars. Building a net fence around your garden will take a few hours.
Bend the garden fencing into an L-shape. Hold a piece of it up to the top of your garden fence so that the part with the larger squares is on the bottom pointing down and the part with the smaller squares sticks out from the fence. Hammer the U-shaped nails into the fence around the wire of the garden fence, which will hold the garden fence in place. Do this all around the perimeter of your fence. You can cut excess wires in the corners with the wire cutters.
Spread the netting over the top of the garden fencing and wrap it around the fencing. With the nail gun, nail the netting to your fence both on top of the garden fencing and the bottom.
If you have trees or sheds or anything a cat might climb to get over the fence, you can use the fencing technique on these surfaces to keep the cat in the garden without escaping.
Keep an eye on your cat for the first few days as she explores the garden. She might find nooks or crannies to get through that you hadn't noticed. Fix them accordingly. Be sure your cat can't get under the fence, either. You can use the nail gun to fasten netting over any holes you see, or drive garden fencing into the ground so that it stands over the hole.
You might want to get extra fencing and netting in case you need more than you estimate.