I just tried this again today on my 55 lb. dog and it just doesn't work. The harness wiggles loose and I have to continually tighten it and readjust the snap. Fortunately she's a good dog and will stop and let me adjust it, but within two minutes, it's worked loose again and I have to again tighten it. She's a lab-boxer mix, so she has a strong chest and she just ignores the pulling under her front legs. When she saw a squirrel at the end of the walk, she maneuvered her head out of the harness, and it was only my voice command that kept her from running after it. For a strong dog, it's totally ineffective.