I just wanted to mention that they do make doggie sunscreen, you can find it at pet stores. But due to the heat, his time outside should be limited anyway. You can also dress him in a wet t-shirt (soaked in cool, but not ice cold water) to keep him cooler and his skin protected. If his skin seems irritated, red, bumpy, raw, you can try giving him a bath with an oatmeal or cucumber dog shampoo to help him feel more comfy.
Is your avatar his picture? He's cute.