I made one for the Kaholo I built for my daughter. Couple #8 oval head screws w/finish washers thru a doubled over webstrap mounted at the tail, 4mm line long enough, and then I stretched a couple feet of 4mm bungee out and stitched it to the line. Result, bungee snaked the aft part of the line up so it wasn't dragging over the side or getting under foot.  I seem to recall total  extended length was around 10'.  Works great - proven by actual test *splash down*.  Oh yes, attachment to leg was a velcro strap I picked up at Wal Mart, pack of four for organizing lines for camping or boating.

Clever! So no real need to go longer than 10 feet, even for a 14 foot board?

Actually I don't have a clue how long a leash is supposed to be RE board lengt so 10' was a Wild A-- Guess.  I wanted it long enough for the person could be clear of the board but short enoiugh so that it get in the way while on the board or drag over the side so I added bungee to collect the excess in a snaky way. 

Aloha ctwiggs. Maybe this info will help. After 40 years of surfing in Hawaii you can expect to fall off either a sup or a surfboard or any tool such as this. If your leash is shorter than the equipment you are riding it will have a tendency to either hit you in the head or face when you surface from your fall. When your leash is a slight bit longer it has a tendency to keep the tool/equipment away from your face and you can have a little more time to block and always cover your face, head , when surfacing. We surf on everything and anything in my48 yrs of ocean fun. Spare no exspence when it comes to a good leash.... agreat surf leash can tow a injured buddy to shore, it can save you priceless hrs of work loosing it on a jagged rock line. I hope I helped.

Yes, William, you make good sense. I am going for a coiled leash so it will be long enough to do he job but still stay out of the way. After building the board from plans and building the paddle from common sense, I have no desire to build a leash. 

Thanks for the help!