AMF, Mindblank (possibly, depending on DM interpretation), Nondetection (again, possibly, depending on DM interpretation), or a custom item that does it, for DM Fiat.
Easiest way around it is the Favored Enemy Arcanists ability, since it specifically only works on creatures who cast spells or invocations, but not spell-like abilities and such. Just don't use anything that casts spells or uses invocations.