Lock out root writes on mounted directory?

[Eric "Shubes"]

I've created a sandbox for building rpms. It was suggested to me that for 
some directories, such as /bin, /lib, /sbin, I could mount them with ro,bind 
options instead of coping or hard linking them. What I've discovered, 
though, is that the ro mount option does not prohibit root from modifying a 
mounted directory. Is there any way to mount a directory such that root 
cannot write to it?
-- 
-Eric 'shubes'