Best harness for Australian Shepherd puppy

At 11 months your Aussie is still developing — growth plates typically don't close until around 12–18 months, so you're right to think carefully about harness fit right now. The essentials for hiking with a dog are a well-fitting harness, a collapsible water bowl, and depending on the terrain, possibly boots — paw protection on rocky or hot ground is more important than most people realise. To point you toward the right harness, it would help to know: how much does your dog weigh currently, what terrain are you hiking on, and how long are your typical hikes?

Good context — 18kg is solidly in medium territory for an Aussie at this age, and moorland means mixed surfaces, some boggy ground, and probably a fair amount of scrambling. For a dog still growing, the main thing to avoid is a harness with a rigid front chest piece or tight cross-straps that sit right over the shoulder joint, because those can interfere with natural gait if they're digging in. You want something with a Y-shaped front that sits in the sternum rather than across the shoulder. Is she particularly active or reactive on the trail — does she pull much?

That's ideal — she doesn't need anything with front-clip anti-pull features, which often put pressure exactly where you don't want it on a young dog's chest. My recommendation is the Ruffwear Front Range Harness. It has a padded Y-front chest piece that keeps the shoulder joint completely clear, two leash attachment points (back and front if you ever need it), and it's built for all-day outdoor use. It's also fully adjustable across four points, which matters because Aussies can be tricky to fit — deep chest, narrower waist. For her size you'd likely be in a medium. It's widely available on Amazon UK and holds up well to mud and wet, which you'll appreciate on Scottish moorland.

Buy for where she is now and adjust as she fills out — don't size up hoping to grow into it, because a loose harness shifts around and can cause chafing, and it defeats the purpose of a proper fit. The Front Range has enough adjustment range that if she puts on another kilo or two in the next few months, you'll almost certainly still be in the same size. If she ends up noticeably bigger than expected, the four adjustment points give you room. Measure her girth just behind her front legs before ordering — that's the critical measurement for this harness.

Good plan. One last thing worth knowing for Scottish moorland: check her paws after longer hikes, especially in summer when the ground bakes and the heather can be coarse. Boots are overkill for most woodland days, but a tin of paw balm is worth keeping in your pack. Enjoy the trails — Aussies are brilliant hiking dogs.