Could random monster spawning be abit more controlled , not spawning next to my mine and destroying it at the same turn end, maybe the monsters only spawning farther from civilization unless "someone finds an old outpost and in exploring it releases the monsters" ofcourse then the monsters should spawn in proximity to the outpost and spread from there. Maybe have an explorable inderground carvern the monsters are coming from and you have to go through it and close the spawning point?

So not an explorable point found by research but a truely random discovery, ie crap happens, so deal with it , it would also split the person who's territory it shows up in attention becuase they need to take care of it quickly or get overrun. I would suggest the monsters not range too far from it, unless attacked and they hunt the hunters.