Dog leads
A lead is a load bearing piece. Construction matters more than pattern, and the hardware is the part that decides whether it holds.
Length
A standard walking lead runs between 120 and 180 centimetres, measured from the hook to the end of the handle. Training leads run much longer; city leads shorter.
Construction
A round braid in four, six or eight strands gives a lead that runs through the hand. A herringbone or half round braid gives a flatter piece with more grip. PPM rope with a splice is the lightest option and the fastest to make.
Handle
The handle should take a gloved hand without pinching. Whipping the join keeps it neat, and a swivel at the hook end stops the lead twisting during a walk.
Buying
Rope, hooks and swivels are listed here: PPM rope (https://www.123paracord.co.uk/ppm-rope/) and swivels and hooks (https://www.123paracord.co.uk/paracord-supplies-and-accessories/swivel/).