[Taqwus]

Problem with the 'guardian monster' concept is that currently, they don't. You can even let them automatically replenish forces (via Soul Contracts for free devils, for instance; or maybe one of the freespawning pretender types?) but they won't stop a Black Servant from sitting around with a Bane Venom Charm, or catch the massed Valkyries led by a Dis.

It'd also be useful for various map concepts if independents patrolled; perhaps even more interesting if some areas could be designated as 'no-teleport' zones or 'cannot fly into here' (cave provinces in general?). An underworld where you -must- fight you way through the hard way, because your mages don't know the precise locations and therefore can't teleport there, or where if you're going to be sneaking you risk being caught -- that'd be fun.