Harness training a Mastiff puppy early

Starting harness work at 9 weeks with a Mastiff is exactly the right call — you want wearing a harness to feel completely normal before they're 50kg and have opinions about it. Harness fit is everything at any age, but with giant breeds it becomes critical fast: a poorly fitted harness restricts shoulder movement, causes chafing under the armpits, and if it doesn't sit right now, they'll learn to resent it. The right type depends on what you're building toward — back-clip for relaxed association-building, front-clip for when pulling starts to matter, dual-clip for long-term versatility. So: how much does your Mastiff pup weigh right now, and what's the chest circumference if you've measured — and is the goal purely positive introduction at this stage, or are you already thinking about managing leash manners as they grow?

Good thinking. At 8kg he's already got some size to him, and Mastiff puppies grow fast — you might only get a few months out of any harness before he sizes out of it, so I wouldn't invest in the largest, most expensive option right now. What I'd focus on at this stage is something with a clean, simple fit — no complicated straps or tightening mechanisms — because the fewer fiddly bits, the easier it is to put on and take off repeatedly, which is the whole point of positive association training: on, treat, off, treat, repeat. Can you take a rough chest measurement for me? Just behind the front legs with a soft tape. That'll tell us which size to go for.

Perfect, that's really useful. At 52cm chest and 8kg, I'd go with the Ruffwear Front Range Harness in size Medium. It's a dual-clip design — back and front — but at this stage you'll just use the back clip for relaxed intro sessions. What makes it right for this specific job: it has two padded contact points that distribute pressure evenly and won't dig in, the chest and belly straps adjust independently so you can dial in the fit as he fills out, and the webbing is robust enough that this harness will likely see him through a good chunk of his growth before he moves up a size. It's also genuinely easy to slip on and off, which matters enormously when you're doing five short sessions a day to build that positive response. He'll outgrow it eventually — Mastiffs typically end up in XL or XXL — but the Front Range scales well and the fitting habits you build now will make every harness easier for the rest of his life.

Yes, and it's worth checking weekly at this age because they grow that fast. The two key checks: first, you should be able to slide two fingers flat under any strap — if you can't, it's too tight. Second, watch his front leg movement when he walks — if you see any shortening of stride or if he's lifting his front legs higher than normal, the chest strap is likely sitting too far forward onto the shoulder blade and restricting movement. With Mastiffs specifically, also keep an eye on the belly strap as they develop that deep chest — it can go from fitting fine to cutting in surprisingly quickly. When you hit the point where you're on the last adjustment hole, that's your cue to size up rather than wait. The good news is by the time he genuinely outgrows the Medium, you'll have a dog who already thinks harnesses are a completely unremarkable part of life.

Great choice. One last practical tip: when it arrives, let him sniff it and investigate it on the floor for a day before you put it on him — just let it exist in his space with no pressure. Then start with just laying it over his back with no fastening, reward, done. Build up to fully fastened over several short sessions. At 9 weeks his brain is primed to form strong associations, so every calm, rewarded interaction with that harness now is doing real work. You're setting yourself up well for when he's the size of a small sofa.