Here's something to add to the list of awesome things you can build for your cat: a catio. It's a portmanteau of cat + patio, and it's an enclosed outdoor space that lets your cat enjoy the great outdoors, without the attendant risks. If you've got the DIY itch, here a few inspiring projects to get you started. Your neighbors may look askance at your new outdoor room, but your cats will be happy, and that's what matters.
Safe cheap way to keep cat from escaping my back yard. He can jump my 6' privacy fence in a second. Took a while to figure out how to safely stop him. Scared of losing him. Flower Bed Border Fence - Vinyl-coated, 14-gauge galvanized wire. 20ft $9 Unrolled and attached to top of fence. Once secured to fence I hand curved the top inward. My neighbors can't see it above the fence. Later He jumped, touched it, but couldn't get over it or get caught in it. Safe success!