I've just gotten a few filters to start messing around with: a CPOL, 0.6ND and a UV. I've heard from most people that they just leave the UV on all the time. Do you then stack a CPOL or ND on top of the UV when you want to use one of those? If the UV is for protection, then wouldn't it make sense to have that as the last filter though? Instead of the $100 CPol? What do people on here do with their filters?