Hooking render methods to specific fields

[Mackski]

I need to hook to a locked textarea field to modify it's layout at run time, however the field doesn't seem available to hook to?

My code is as follows:

$this->addHookBefore('InputfieldTextarea::render', $this, 'render'); 

public function render(HookEvent $event) {
  $field = $event->object;
  if($field->name == "currency_data") {
    echo "<pre>".$field->value."</pre>";
  }
}

If I modify the field to any other value than "locked" the field becomes available.

Not exactly sure why it's not available when locked.