If you could become a necropolitan (lose level 12, which is unfortunate because level 12 is generally awesome since you get a feat and an ability boost and all your saves and BAB advance, but may be tolerable since you keep 6th level spells), and retrain a feat to Lifesense, he will not be able to hide from you, period. You also shut down his primary means of hurting you, unless your DM is savvy enough to pick up one of those methods of dealing sneak attack to undead. If he has, he'll probably rule you're not immune to death attack (even though you quite clearly are, as it's a Fort save that doesn't affect objects, but I digress).
Once you've found him, use a Belt of Battle (caster's best friend; if you have the dough, buy at least 4 and and put on a new one every combat) to drop a Dimensional Anchor and a domed Wall of Stone. You'll need to find some way to beat that SR, though... Others probably have better advice on that, but Assay Spell Resistance can help, and Arcane Mastery or whatever that feat that lets you take 10 on caster level checks can help you avoid bad rolls. You may need some Celerity cheese to get all these actions off, I dunno. Anyway, once you've got him trapped in there, you have a while to figure out what you're going to do.