Watermarking - making permanent (unremovable)

I have noticed that if I add a watermark and "fix" it by:

Print production > Flattener preview > All pages in document > Apply

Acrobat often (but not always) doubles the number of pages in the document. What is even more irritating is that it doesn't just add a complete copy of the document after the original, making it very time consuming and trick to manually remove unwanted pages.

I have overcome this issue by making sure that I redact the document before adding watermark, and that this seems to permanently fix the watermark. If I don't need to redact anyting, I make a tiny square of redaction to enable me to permanently "apply" the unnecessary redaction. This has worked well until now, when a colleague has tried to do the same but is still able to remove the watermark afterwards.

Please, please, please make it easier to apply a PERMANENT watermark.