The sunscreen I most trust to keep the painful and expensive art on my arm from fading is La Roche-Posay's Anthelios 60 Melt-In Milk.
Consistently one of Consumer Reports' best sunscreens, my far less scientific experience has shown it to be super effective. There are several 60 SPF concoctions by La Roche-Posay, and all are good, but the Melt-In Milk seems to be the one to use when covering up an arm or leg. I have some thinner stuff they make for my face, as the Milk takes a bit to melt in. Even with a minute or two of massaging, the white paste remains a bit visible until I've been in the sun for a few moments.
I don't claim this is the only sunscreen I use, as if I don't have it handy I will put on just about anything to avoid a sunburn. I burn easily and have repeatedly made mistakes in my life that left me with open wounds.
Sunscreen is your friend! Be careful about which products you choose when you are going into the ocean. Water-resistant doesn't mean friendly to the ecosystem you are swimming in. I believe the chemicals in this, and many, many other sunscreens destroy delicate marine ecosystems.
