We recommend that all Stand Up Paddlers wear a suitable leash when using their board in surf. Although you should not be using your board close to other surfers wearing a leash will allow you to keep contact with your board when you fall and avoid long swims.
Using a leash on flat water is also advisable if you are not a strong swimmer or it is windy.
Look for a leash that is at least as long as your board and that is designed to take the extra weight of an SUP board.
There are a large range of Leashes on the market and all shops selling SUP boards should have a good selection.