Here are a couple of tricks that work against Ermor in certain situations: since Ermor's armies tend to mostly consist of mindless undead, any spells and attacks that don't target them will focus on the commanders. Thus using such spells as soul slay and mind burn or even charm you can destroy all the commanders in a short time. This will in turn result in the army dissolving. In my experience this is a very cheap and effective tactic against an unprepared Ermor. (There are of course counters, as for all tactics.) Note that Ermor's PD has ghouls (or at least it did in Dom2) which do suck up the spells, so this is more of a defensive trick.
In a similar vein, mind hunt is pretty powerful in stopping Ermor armies: of course, that takes a couple gems per casting and you'll want to have penetration items on the mages, but it's still a cost-effective measure if only for dividing Ermor's army before a large assault by killing off a couple commanders which leaves their underlings to the province of origin. (This, again, can be countered with a bit of planning by Ermor.)
Attacking the problem from another angle, equipping thugs with fire shield and making sure they are tough enough to withstand a multitude of attacks by mundane weapons (that are Ermor's mainstay) is an effective way to kill masses of undead. It's not really an early game solution, though, unless you happen to have a pretender with fire magic. More generally, if you can field a thug that can survive until the end of the battle, you can kill Ermor's army by making its commanders rout if you're the defender. (Body ethereal, protection over 20 and some regeneration is a good start; it's also essential to make sure there's enough reinvigoration to prevent fatigue from accruing.) In practice it's not very easy to field a thug like that very early especially with Late Age nations, but later on you really should make sure to have some.
To get even more nation-specific, there are sacreds that can beat very large numbers of Ermor troops even severely outnumbered. To name a couple of examples, T'ien C'hi's sacreds with E9N4-bless will kill untold amounts of undead if managed properly (coupled with their other strength, powerful PD
, they are indeed quite an effective nation against Ermor). Pangaea's Black Centaurs also present a very effective fighting force that can be massed to beat any size of Ermor armies early on. There are other sacreds that I wouldn't hesitate to pitch against the undead horde, as well. (Of course, a competent Ermor will find a way to lure your troops into a battle where he has a sufficiently large numerical superiority and kill you off, or find another counter.)
There is no one size fits all -solution to beating Ermor, the same as any other nation. Every nation has
some thing they can try, though.
[On a completely unrelated note, I find it crass in the extreme to moderate in so hamhanded a way in the public. If you want to threaten Bob or anyone else with various sanctions, I for one would appreciate it being done in private.]