This discussion reminds me of my youth.

Sex on the beach or just outdoors always had its issues, the biggest wasn't sand but sun. Sun tanning lotion was not really a good lube either. I can also remember spending days in severe pain with the burns in the weeks after and that not so enjoyable feeling waking in the morning on a layer of dry peeled skin. Back in those days we didn't have effective sun block unless it was zinc cream.