WorldGuard Block Restricter adds two (six) flags to WorldGuard regions:
It requires WorldGuard Custom Flags.
Simply use these flag as any other WorldGuard flag:
/region flag restriction deny-blocks obsidian, cobblestone
You can also use "any" to block any block placement/destruction. This is usefull for whitelisting, because allow-blocks will overwrite this.
/region flag only-dirt deny-blocks any
/region flag only-dirt allow-blocks dirt
From version 1.7 on you can also use block/item ids.
Click here for some other plugins using WorldGuard Custom Flags.
If you have problems with this plugin read the F.A.Q.. If this did not help you, you can receive help here.