Dakine are renowned for making quality surf goods and in particular seriously strong surf leashes.
Dimensions: 9'6'' x 1/4" [ 2.89m x 6.5mm ]
Here's what Dakine say about the Longboard Knee leash.
The Dakine Longboard calf leash gives you room to roam on your longboard. At 9' 6", it lets you ride the nose and the calf cuff helps reduce cord wrap at your feet. Maximum strength 1/4-inch (6.5mm) urethane Dura-Cord can handle up to a couple feet overhead. The design is made for easy movement, long-lasting durability and comfort.