I have a 57 lb Golden Retriever/Cocker Spaniel mix. He looks exactly like a Golden with normal proportions, just slightly smaller than average. That said, I cannot get this harness to fit him right in either a medium or a large. He should be a large according to the size chart, so that's what I bought first. The chest straps fit fine, but the neck was ridiculously loose even when I tightened the straps as much as possible, so I ordered a medium to try. With the medium, the chest straps are just a bit too tight, and oddly, the neck is still slightly loose. I started wondering if maybe it was loose on purpose to create more room for items in the backpack, so I stuffed it full, yet the looseness persists. We've used at least 6 or 7 harnesses in the past and have never had fit issues, so I don't know what's going on. I keep thinking I'm missing an adjustment point on the neck, but I can't find more than the two on either side. These fit issues are especially disappointing because this is otherwise the perfect harness for us. We like to run, but we live in Southern California where it is way too hot all the time, so I wanted some way to carry water. I got a Ruffwear Switchbak, but you have to fill both sides of the pack with equal weight, which was a hassle and seemed too heavy for running in the hotter months. This harness is more appropriate for exercise, and even though the pouch doesn't hold much, it fits either of my flexible water bottles (a Vapur Shades 0.5 L and a Vapur Kids 0.4 L, though I'd recommend the kids one since the cap takes up way less room) as long as they're only about half filled. We don't do huge runs, so having just a bit is enough for my peace of mind. When I'm not bringing water, I can fit my phone, my keys, some extra poop bags, and my albuterol inhaler. It probably wouldn't fit a ball large enough for my dog, but maybe for a smaller dog--although I will say that the pouch on the medium seems a bit smaller than the one on the large, so that may not pan out. Either way, it's really nice to have your dog carry the small essentials, especially when you don't have pockets! It's also very well made and seems comfortable and breathable. I like it enough that I'm leaning towards keeping the large and paying someone to shorten the neck straps, but I'm not happy about it because that will probably double the cost of the harness for me. However, I haven't found another trustworthy brand that sells a single-pouch backpack harness, so I might just have to suck it up.
