Make a 'last updated' field read-only

[jitsobullet]

Hi All,

I wish to add the 'Last updated' fields to the Virtual Machine CI, which i have and it provides a timestamp on update, however the problem is i cannot make this a read-only field.
Currently i am using the following:

~~~~~~~~
MetaModel::Init_DefineState(
"new",
array(
"attribute_inherit" => '',
"attribute_list" => array(

                'last_update' => OPT_ATT_READONLY,
            ),
        )
    );

~~~~~~~

Any ideas?

Kind regards