[Taqwus]

Etimmu can summon ghosts, if memory serves, which should be decently resistant to banishment. It's only one a turn IIRC. If you do send him into melee, the fear-causing helmet would be a nice touch. If his priests are busy doing Sermon of Courage, they're not busy banishing.

Lizard Kings need a temple and money; if you raid, setting taxes to 200% and pillaging whenever given the chance, they'll contribute less to his economy even if you need to vacate the province. So would infiltrating Black Servants w/ Bane Venom Charms, if you've got the gems.

I'm across the country from my manual right now, so I can't look up the research requirements, but if your Dusk Elders can cast AOE morale-dropping spells, that may help clear a path through whatever screen (predator lizards, say) that he's put up.