Best location for Dexcom sensor. Ironically, they and the FDA don't officially approve it, but it still works. Putting them on the upper arms works almost as well as this, but is not quite as secure. Can't be a Dexcom Warrior if you do this because that would get Dexcom in deep shit with the FDA.
On the plus side, paddle boarding is one of the sports that's compatible with social distancing and friendly for those with diabetes because you can keep and carry what ever you need with you.