Under SQL Server 2005, the add_server_role_member and drop_server_role_member may only be used with event notification and cannot be used with DDL Triggers. The reasoning is that since only a login with sysadmin rights can affect server role membership and a sysadmin can always disable the trigger, triggers are not reliable.

However, SQL Server 2008 10.0.1075, does support triggers on the server role membership event.