I use a harness for Emmers. Its great. He gets his outside time and I don't have to worry about him getting hurt. Its nice in the summer to sit outside with a book and have him chasing bugs and playing in the grass.
We take several of our cats out on harness and leash, too. They got used ot it surprisingly quickly! We got the retractable leashes that they sell for dogs, they extend to 20 feet so if the cat sees a squirrel and decides to chase, it doesn't get choked and pulled back. And Lil will climb a tree for a few feet, still on a leash.