...there's no clear way within the law to actually declare something in the public domain. Instead, the public domain declarations are really more of a promise not to make use of the exclusionary rights provided under copyright.
Ok, so the statement is about a clear way to put something in the public domain. Here's how you clearly put something in within the law: (1) You declare it public domain. (2) Now, keeping it there: You simply exercise a level of ethics even a 5 year old understands: You don't go back on your word, because (for one thing) that would make you a major fucktarded scumbag. (3) Whatever it is, is in the public domain, stays there, totally within the law, end of story.
Sometimes the ideas of law -- which is a hugely flawed instrument -- and the result of actions taken/not-taken get all confused in people's minds. If you want to put something into the public domain, do so, and subsequently just exercise a minimal level of personal honor, and you can be sure that your intent will carry through. The only one who can screw this up is you, and to do that you have to act in a particular way which guarantees you are knowingly acting like a dickhead. So when this clown tells you that you can't get it done, he is impugning your honor, not describing reality, and the only reaction you should have to that is annoyance.
Given that you are honorable and simply don't go back on your word, the user has nothing to worry about either.
So this really isn't about law. This is about your behavior.
Now, I grant you that most an entire generation having grown up with the idea that it's ok to steal IP, and the toxic idiocy of the "information wants to be free" crowd additionally muddying the waters, and the proliferation of people who just can't seem to keep their word, one might have reason to be cynical about this. But remember: TFS is saying that it is hard to put something into PD. It isn't. There's no reason you or I have to act without honor, and there are many reasons, starting from simply sleeping better at night, that we ought to act with honor.
Yes, I've got stuff out there that is PD. No, I will never, ever revoke that status. See how easy that is? 100% effective, too.