Answer:
I'm not man's best friend, I'm their enemy, I can mark your end, yet you do not see me, I am very small, but very tough, If you have me, then you have it rough.
What moves without seeing and cries without eyes?
You can only have it once you have given it.
Through its wounds, water does run. It once held many but now has none. What is it?
As soft as silk, as white as milk, as bitter as gall, a thick green wall, and a green coat covers me all.
What never gets any wetter no matter how hard it rains?