If you can... pull the rocks OUT of your tank. Xenia can put off some nasty stuff. If you can avoid cutting or tearing it off in your tank, IMO, you should. If you can't, put in fresh carbon to keep the allelopathic chemicals in check.
You can try to nudge the base or "foot" off the rock with a credit card, or your thumb nail. Then, reattach it to a frag plug, or just bag it.
You could try trading with local refers, or to your LFS.
*If you haven't had it out of your tank yet, into the open air... It smells REALLY, REALLY, REALLY BAD!
Best of luck, I had/have the same problem.