If you have a dog that is not docile the clasp can unsnap. I have a 2 year old stubborn French Bulldog the clasp unsnapped x2, the first time I assumed I didn't double check it cause it seemed impossible. My dog is a runner and very strong so I check and recheck before each walk, I did my usual 3 checks and we started walking and it just busted open. This is dangerous for runners, I live downtown Chicago I could have lost my dog to traffic/accident if I didn't literally jump on him before he noticed he was free. Now with a sprained wrist I write to warn others. The design is great, will research other companies with similar design but perhaps one without an all plastic buckle. User's recommendation: Do not purchase if your dog is a runner.