If you put anything on top of snow, just use grit. That's what they do in countries where there is too much snow, or it is too cold to melt it with salt. If you clear the snow first, a bit of salt (or rock salt which is only dirty salt) will melt everything that is left and will melt small subsequent falls. Chucking (rock) salt on top of the snow is a pointless waste unless the snow layer is very thin.