Securing Postgres

I would like to secure Postgres completly.

Some issues that I don't know you to fix:
1.  User postgres can use psql (...) to do anything.
2.  User root can su to postgres and thus do anything.
3. Disable all tools like pg_dump

How do I secure a database if I don't trust the administrators.
The administrator will not break the db but they may not view
any information in the databse.

Regards

Lani