Use the dead rock on the bottom and then place the
LR on top of that. You could easily use half the total amount as dead base, 50/50 mix. Then you could purchase one type of base rock on-line or get several different types from the
LFS which would increase the bio-diversity.
On-line rock is usually the best if you are looking for "extra's", critters, corals and such. The
LFS rock will still have many organisms but not the same amount or types that "raw"
LR would.
Cheers
Steve