Lifetime of Live Rock

[steveg]

Hi there, maybe this is a silly question but I am curious to get some ideas on this:

Does live rock have a lifespan whereafter it will not perform the required function in a tank system and if so how frequently should one replace the rock in a system?

I have heard that 5 years is a reasonable time for fresh rock to be useful for, anyone had a tank for longer than that without changing any of the rock?

I look forward to your replies on this one.

Thanks

Steve