Default views argument that can't be overriden?
If the "User: Current" filter is not an option for you, then you can use a hook_views_pre_execute() to modify the argument before the query is run.

In your custom module (assuming you have one argument):

function mymodule_views_pre_execute($view) {
    switch($view-&gt;name) {
        case 'name_of_view':
            global $user;
                if ($view-&gt;arg[0] != $user-&gt;uid) {
                    $view-&gt;build_info['query_args'][0] = $user-&gt;uid;
                }
            break;
    }
}


Even if a different argument is supplied in the URL, the current user's id will still be fed back into the view.