My top covering experiments have come around in circle - back to tarp.
It doesn't have to be difficult, and is very cheap. Just get some tarp rolled out over the top of the stack row (cut a big wide one in strips the right size if you don't have the right width), then put another layer of wood on top of it. The top layer of wood holds the tarp in place, and it'll also dry while it's up there too. If you pay attention to how you stack the stack, you can end up with it being higher in the middle than the edges so water will run off.
No tieing, stapling, roping, screwing or anything else.
Last fall I did that, and also tried some roll roofing. Can't find rubber stuff here, only asphalt. Both made it through the winter, but the rolled stuff is showing cracks. The tarp stuff is still in place just the way it was in the fall - and it was a heck of a winter, piles of snow & every snowfall was a blizzard. The top layer of wood will also block most of the sun from sun-damaging the tarp.
Another hint for stacking in rows on pallets - orient the rows so prevailing winds hit the end of the row, as opposed to blowing through the stacks. The rain will only hit the end of the row, and stay out of almost all of the wood. The wind blowing across the ends of the wood will still pull moisture out.