How do we prevent "obsolete" tags from being used in subsequent questions?

Question

(I am sure this has been answered already for the StackExchange system, but it is worth asking here if for no other reason than as a reference to an answer that already exists.)

Related to this question about merging tags and removing obsolete ones, say we decide us-census is obsolete and should not be used. How do we prevent new questions from being asked with the obsolete tag? Can we mark them in the system as never to be used (and better yet, that it has replaced by e.g., usa and census-records)?

Answer 1

http://blog.stackoverflow.com/2010/08/tag-folksonomy-and-tag-synonyms/ and What are tag synonyms and merged tags? How do they work? seem relevant. A tag synonym linking us-census to census-records should prevent us-census from reappearing. Can't see any way to replace one tag by two though.