ORA-13505

I tested this on an Oracle 10 database running on Linux. If you try to make the SYSAUX tablespace READ ONLY, you get an error. There is no way round this, you cannot do it: 

SQL> alter tablespace sysaux read only

  2  /
alter tablespace sysaux read only
*
ERROR at line 1:
ORA-13505: SYSAUX tablespace can not be made read only

SQL>