In order to find myself some nice lapis lazuli and get away from my current base, I’m building a little tunnel in the Nether to allow me to get into the midst of some fresh chunks fairly quickly.
I have a nice little stone house, but as Ghasts and zombie pigmen can spawn at “any light level” in the Nether, how do I keep them from popping up in my Nether regions where I don’t want them? Will they even spawn on “foreign” blocks (e.g. those that aren’t Netherrack, slow sand, etc.)
As of the Halloween Update:
You don’t have to worry about Zombie Pigmen (they are, after all, neutral mobs until provoked).
Ghasts can safely be kept out by restricting yourself to not using any of the 4x4x4 (or larger!) areas that they need to spawn. Keep a tight ceiling, and you’ll be fine.