A few things to remember: Your leash needs to be at least as long as your surfboard. This allows enough room between you and your board when you fall. If your leash is too short, you'll find yourself being hit with your surfboard. Also, the thicker the leash is, the greater the drag. For surfing small waves, it's sensible to get a thinner leash which will create less drag and make it easier to catch waves. For everyday use or when surfing in bigger waves, it's best to get a thicker leash. A thicker leash is less likely to snap and will last longer.