Part 6: Of Goblins

I'm finally at the stage in the design process where I get to start thinking about monsters and movements and populations.  Designing a Mega-Dungeon is very different than designing a standard one.  Currently, I'm writing the first "module" and need some solutions to problems that do not present themselves in a standard dungeon.  Mostly its about goblins.

See, gobbos hate dwarves, and dwarves hate gobbos.  So, it stands to reason, that they would kill each other on sight every time.  They are close to where the dwarves still hold their land, so it would stand to reason the dwarves would just walk out there and kill them.  The problem is, then, that the PCs would not be able to kill any goblins, because they are all dead.  So, I need a reason why they are not all dead.  And there is the crux of my problem.

I have come up with a few clunky solutions to this problem.  I'm not sure which I will use, but I find this writing dilemma interesting enough to share.  So, the ideas:

1. A magic portal to another area where gobbos breed, then send in the males to become warriors.  This portal would be a threshold that would require goblin blood to cross.  I'm not sure if it would stay open, open with a command or at set times.
2. An outside force periodically restocks the gobbos.  They are put there by a BBM and used as eyes and ears to keep track of how many/what kinds of adventurers are storming the mountain.  This may be the most conducive way to integrate the theme (isolation) and the story.
3. A huge warren of goblins lives somewhere nearby, undiscovered.  Occasionally, they are too big for the place they are, and a new group of gobbos heads out.  The place they settle (every time) is great until the adventurers come in and destroy them.

Any of these that people like more than others, and why?  Anything else that I haven't thought of?