I'm going to show you how to make a custom sized, personalized, and nearly indestructible dog harness using para-cord and a crochet hook.
Step 1: Crochet dog harness
Dog (or cat, or, whatever pet you need to put a leash on)
Para-cord / Nylon twine (I'd suggest against cotton, or, hemp, because they tend to rot.)
Hardware (buckle, clip, clasp, etc.)
Optional (measuring tape, lighter, yarn or embroidery needle)