Is there a way to become immune to Possession all the time?

I’m going to be running an Eberron game soon, and one of the players has expressed an interest in playing one of the Inspired ‘gone rogue’. Unfortunately, the rules for Possession of the Inspired are … Very much in favor of the Quori.

I can always come up with a custom item, but is there a way to become immune to possession more or less all the time in 3.5? Answers that work from moderate levels are preferred, but anything that works will give me something to work with.

I am looking for pre-existing solutions which are rules legal as a starting point.