This article gives instructions for installing zinc strips at the ridgeline to inhibit moss.
This picture shows nails through the zinc strip:
It looks like they have nailed through the zinc in to the roof. Wouldn't that allow water through the roof?
(Posted for a friend. I don't actually have a roof. :-))
Best Answer
Nail them down, the same way your shingles are nailed down. That is, you nail down a course of shingles, then lay down the new course above the last course, working up the roof. This way the next course hides the nails holding down the previous one. At the ridge, before a ridge cap goes on, you also nail down the zinc strips, placed so they will protrude beyond the ridge cap. Finally, the ridge cap goes on. Enough of the zinc protrudes so that the metal gradually leaches out with every rain to impede moss accumulation.