Undead enemies such as Zombies and
Skeletons will not cross a path that has a puddle of holy water in it.
You will first encounter zombies in the ship at the docks (you need
glyph door ability to get in) most zombies will withstand most attacks I
use Fire arrows which will kill almost instantly. Fire arrows can be
found at pretty much any fence unlike holy water which require good
standing with the Hammerites and access to fort Ironword or w/e.