Bob,

How did you test your hypothesis. I suspect you tried to select from a
SYSCAT view or a SYSIBM table.
By default PUBLIC gets granted SELECT on the catalog objects (SYSCAT,
SYSIBM, SYSFUN and SYSPROC).
In DB2 9 there is a new RESTRICT option that creates the database very
tight to begin with.
On DB2 V8 a simple procedure revoking SEELCT from PUBLIC on these
objects should do just fine.
Something like:
CREATE PROCEDURE revokepublic(IN objecttype VARCHAR(20))
BEGIN
  DECLARE revtxt VARCHAR(1000);
  DECLARE curtxt VARCHAR(1000);
  DECLARE SQLCODE  INTEGER;
  DECLARE SQLSTATE CHAR(5);
  DECLARE objname VARCHAR(128);
  DECLARE objschema VARCHAR(128);
  DECLARE stmt STATEMENT;
  DELCARE cur CURSOR FOR stmt;
  SET curtxt = CASE UCASE(objecttype) WHEN 'TABLE'
               THEN 'SELECT TABSCHEMA, TABNAME FROM SYSCAT.TABLES WHERE
TABSCHEMA LIKE ''SYS%'''
               ...
               END;
  PREPARE stmt FROM curtxt;
  OPEN cur;
  LOOP
    FETCH TABSCHEMA, TABNAME INTO OBJSCHEMA, OBJNAME;
    IF SQLCODE = 100 THEN LEAVE; END IF;
    SET revtxt = 'REVOKE SELECT ON ' || objtype || ' "' || objschema ||
'"."' || objname || '" FROM PUBLIC';
    EXECUTE IMMEDIATE revtxt;
  END LOOP;
END

Well, something like that....

Cheers
Serge