A couple of things: I think the SPF 70 is Neutrogena? That stuff is great.
Also, make sure that your sunscreen has UVA protection. It doesn't matter if it's SPF 2 billion if it's only UVB ... UVA is what scientists believe causes melanoma.
This is why there is no proven link between sunscreen use and lowered rates of melanoma. In some studies, people with melanoma actually used MORE sunscreen than those without. Outside workers also have a lower rate of melanoma than inside workers.
Speculation is that if you aren't burning (caused by UVB rays), you'll stay out in the sun longer, absorbing more UVA rays (which, melanoma-wise, are the ones to worry about). And that people with fairer skin (who burn more, ie, are more susceptible to melanoma) use more sunscreen than those with darker skin. So it's not saying that sunscreen causes melanoma. Ha ha. But it has never been proved to prevent it. It does prevent burns and premature aging, etc, and has been shown to reduce non-melanoma cancers (basal, squamous cell).
But, just like wearing a helmet isn't necessarily going to help if you run into a lift tower at 30 mph, using regular sunscreen doesn't necessarily help guard against melanoma.
(And, once again, I am not discouraging the use of either! Just be educated about their limits.)