[Delphinus]

I agree with Brad but to add to the thoughts I think it's possible to somewhat "renew" rock by "cooking" the rock (by "cooking" I mean sit in a livestock-less but still seawater environment and not "place the rock in a pot and put it on the stove" .. I've never really liked the term "cooking" for live rock because of that imagery). After cooking for a few months a lot of the initial critters will need to be reseeded though.

In my own experience using rock that had been dried and left outside for a period of time, that rock was nowhere near as effective in maintaining a healthy reef as fresh rock would have been. It does the job but it took much, much longer for this tank to establish itself and hit a healthy groove. And at that, I have to be much more aggressive with nutrient management than I have with previous tanks. So I am totally convinced that live rock can have an effective lifespan. At least with cooking it though it can be salvaged as I think it's a total shame to see rock end up in the garden just because it hit "X" number of years old..