Just become a hipster and you will not need one. Problem solved

Never used one so really I have nothing to add to this thread. But google it and you can find some gold
Leash selection. One of the best longboard tips you will ever hear has to do with leash selection and the choice of whether or not to wear a leash. Ideally, in classic longboarding, it is best to not wear a leash at all. Going leash-less not only looks classically cool, it also frees up your feet to cross-step and go switch without getting tangled. If you must use a leash but still want the freedom to walk the board, it is best to purchase a longboard leash that attaches to your upper calf. Calf leashes free up the rider’s feet, which makes it easy to move around on the board. Beginners should always wear a leash. Remember, the leash must always be longer than the board you are riding, and leashes are always fastened to the back foot.