go here:
bestskinsever.com
and buy the skin for the zvm.
Follow the installation instructions carefully and to the best of your ability.
Using this "skin," which is truly invisible, if installed correctly, your player will not be scratched at all, no matter what case you use. I use it, and have used it on my zvm, and cell phone, and have not had any problems, for almost a year now.
It will not leave a sticky goop if you try to remove it, I have personally had to remove one (for an RMA), and no goop was left (after 7 months of use).
Silicone skins will always end up scratching the device somehow, unless you use the product I linked to, or an Invisible shield (which is the exact same thing as the best skin ever, only it costs a lot more, and I don't know if you can order one oustide of the US).
Actually, the silicone skin itself does not scratch the player, but instead, particles of dust and dirt get in between the skin and the player, then the skin moves ever so slightly, and pushes the dirt/dust into the surface of the device, causing the scratch.
A leather case may also cause scratching to the player
My reccomendation:
Best Skin Ever for scratch protection
+
a leather case for drop protection
=
one happy ZVM