Additional field to #__user

[awethumb]

When a user registers, I need to add to my ref column.
I had tried to place this in classes near line 177

$query = 'UPDATE #__users SET email='.$db->Quote($generated_details['email']).',ref=999 WHERE id='.$db->Quote($user_id);

Should I be trying this somewhere else?
I have been picking around at it with no luck.
Any hints would be appreciated.