Been romping with my Undead until...

Spells like:

Antimagic (Astral, Enchantment 4)

Drain 2

Unholy Priest Spells like Unholy Protection.

Also try fighting in your domain.

Each of those increase your MR of your armies. Though Ermors troops are usually fodder and used to distract while your mages and elite troops tear up the armies.