I have an aussie/lab mix and she has a very awkwardly shaped body. She can't walk on a collar, not because she pulls on the leash, but because she has a fat neck and tiny head and can just slip out of it. She has a harness before this one that was a "step-in" and it was a pain to put on, and never seemed adjusted properly. It dug into her armpits too. This one is padded, goes on over the head and was easier to adjust to her weird proportions. It also doesn't twist around like the last one did, and doesn't dig into her pits