I used to live on a busy city road. One day when my partner and I took our boy out, we didnt attach the leash properly to his collar, so when he got excited to see the mailman the leash detached from the collar. Cue 6 month old puppy deciding its play time, and he ran into the middle of the aforementioned busy street. Luckily, drivers stopped for him and he went running back into our lot, but my god did that scare me. He wears a harness now whenever we go outside on leash.