Not that it's a poem or that you should try it with your one, but my two oldest boys hated wearing sunscreen. One year, we went to Hawaii. My oldest has my fair skin; his little brother is lucky and tans like my husband.
The oldest burned, his brother didn't, and when they got in a squabble, my oldest learned the hard way why he should wear sunscreen: sunburn slappers.
He's never gone without sunscreen since.
Never have had a problem with my other 4, they don't put up a fight.
If you want him to do it, make sure you set a good example and use it on yourself, and try to make a game of it.