The Keeper of secrets is optimized to kill PCs for sure. As if casting 15th level spells wasn't bad enough, it can counterspell all day long and ignore antimagic fields..... Who said there is no epic challenges in Eberron?

Okay I found a rather definitive way to bind rajahs: Epic dragon magic and sacrifice a few coualts (on endangered species list if not completly extinct already). Massive dragonahards, starting your own religion and moving mountains maybe involved as well.

It makes you wonder how the couatls and dragons managed to seal 30 of them.