If you really want to add anti-piracy:
Release a purposefully 'cracked' and 'buggy' version of your dll to pirate websites (high-cpu usage, frequent crashes, ect). Several versions infact, make them seem as legit as possible. You can even add a time delay to make it seem like it works perfectly at first. Having an already released 'cracked' version of you software will also deter crackers from actually cracking it too since they think its already been done and if they do crack it.. it will be just be mixed in with your version.
This should really frustrate the pirate community. Though, I'm not sure if that will result in more sales for you
Serious Sam 3 did this - Made unbeatable monster show up
Game Dev Tycoon did this - Probably the funniest, where eventually people would pirate your games to the point where you couldn't play anymore. Someone ironically posted to one of the forums and asked if there was some kind of DRM that could be researched that would prevent this
One of the Crysis games did this. It replaced your bullets with chickens that didn't do damange.