The harness is a skill, not an accessory
Cats do not take to harnesses the way dogs take to collars, because pressure around a cat's chest contradicts everything his body expects freedom to mean. Garden adventures succeed when the harness stops being an event at all. That happens indoors, over days, in the rooms where he already feels safe, long before the garden is involved. Rushing this stage is the single most common reason cats freeze, flop onto their sides, slink along walls or back out of a badly fitted harness at the gate, and each bad experience makes the next attempt slower.
Fit and first impressions indoors
Choose a harness designed for cats, ideally a jacket style or a well-fitted H-shape that distributes pressure and cannot be reversed out of easily. Let him sniff it, rub his cheeks on it and find treats beside it for a day or two before it touches him. Then drape it over his back during a meal, fasten it loosely for a minute of play, and build up in short sessions he can end. Adjust until you can slide two fingers underneath at every strap, and watch his walk: a cat mincing like the floor is lava is tolerating, not accepting, and needs shorter sessions rather than encouragement outdoors.
Add the lead before the outdoors
Once he plays, eats and grooms normally while wearing the harness, clip on a light lead indoors and let it trail under supervision, then hold it with no tension while he chooses the route around the room. Practise the feeling of gentle pressure and release so he learns that moving towards the pressure makes it stop, the lesson that prevents panic if he ever startles outside. Keep a treat trail along a hallway to rehearse walking with you rather than being towed, and end every rehearsal with the harness coming off calmly in exchange for food, so removal is not an escape he has to engineer.
First gardens are tiny and escapable
Choose a quiet moment with no dogs, visitors or lawnmowers, carry him out in your arms or let him walk out through an open door, and set him down near cover he can retreat to. Let him stand, sniff and decide; the first outing may be three minutes of sitting in a flowerbed, and that is a success, not a failure. Follow where he leads, keep the lead slack, and go back in before he asks to, leaving him wanting more territory next time. Gradually let him explore further as his body language stays loose, tail up and ears forward, rather than low, scanning and freezing.
Safety habits for every outing
Never tie a cat's lead to a post and leave him, never let him climb trees on a lead where a branch and a fall can trap him, and lift him past anything that frightens him rather than dragging him through it. Check the harness fit each time, since a cat who has lost or gained condition can slip a previously snug strap, and avoid midday heat on hot paving for paws that live indoors. If he bolts despite everything, a collar that identifies him instantly is the difference between a scare and a loss.
Identification that travels with him
Alongside his harness, KinsLe's Verified QR ID Pet Profiles put his own unique QR code on his collar, so anyone who finds him on an adventure gone wrong can scan it and reach his profile and you.