When I started my tank, I used a whole slew of "dead" live rock. It had lived in its previous life in my brother's tank, before it crashed on him. The rock had sat dry for nearly 2 years. I cleaned it good, and them placed it in my tank, interspersed with a few pieces of fresh live rock purchased from the LFS. Now, it all appears to be "Live". Worked great for me, and saved me a whole chunk of change.