Ok, so you want to prevent any DDL being executed in your Oracle DB? You could create read-only accounts but here is another way. Create this trigger:
create or replace trigger no_ddl before ddl on schema begin raise_application_error( -20001, 'DDL execution temporarily not allowed;'); end no_ddl;
All DDL raises an error, except for the ‘drop trigger no_ddl’ by the way.