I've created a StaffPage which lets me add Staff and Departments. BY adding this line below to both staff and department DataObjects I can associate them back to the StaffPage (which obviously, I need to do). They're also associated with each other, so that I can list staff by departments.

public static $has_one = array(
"Parent" => "StaffPage",
);

My question is, how to I stop this field from being included in the data entry form when I create a department or a staff member (I'm using the GridField object).

Thanks in advance, let me know if you need my code.

It was actually ParentID - I found it by inspecting the element but you got me on the right track, thanks very much.