Mother of serpents and tarts

[Finalgenesis]

Pretender is immune to LA ryleh insanity, as is starspawn priest and mage (but not star child and slave mermage). MR does help resist the effect, so if you conjure up a mage to diversify (or roll a N mermage), you may want to stick a AMA on it, or even add a lead shield on top if it's high valued. Even so expect the insanity rate to slow down but not stopped completely.

Otherwise there's no known way to mitigate/cure something already insane or has shattered soul, when they go crazy they there's no stopping it. Maybe keep them in non-key provs where they can't burn down your temples and pillage up the unrest (and boy do tarts add a lot of unrest with just a turn of pillage...).

On the other hand getting lots of cheap insane commanders guarantee a decent supply of prophets (aka walking temples), and you need it even with dom 10 to resist dom kill from the seas seeing as you loss the ability to build or recruit much sooner or later.