harry potter - Did Moody seriously think his defences would keep Snape out of Grimmauld Place?

When the Order of the Phoenix abandoned Grimmauld Place after Snape's supposed betrayal Mad-Eye Moody set up some defences in the hallway. This was to protect Grimmauld Place from Snape and the Death Eaters.

“We can’t expect [the Fidelius Charm] to hold much longer.”
“But surely Snape will have told the Death Eaters the address by now?” asked Harry.
“Well, Mad-Eye set up a couple of curses against Snape in case he turns up there again. We hope they’ll be strong enough both to keep him out and to bind his tongue if he tries to talk about the place, but we can’t be sure. It would have been insane to keep using the place as headquarters now that its protection has become so shaky.”

_{(Deathly Hallows, Chapter 6, The Ghoul in Pyjamas).}

Basically, the curses are two-fold.

• A Tongue-Tying Curse. This was presumably to try and stop Snape breaking the Fidelius Curse.


• A dust-like figure of Dumbledore. This part involved hearing Moody's voice (saying, "Severus Snape?") followed by a deathly dust-shadow projection of Dumbledore. This apparition vanished when one said the word killed. (There's been some confusion on this point so I'm including the following quote to clarify:)
  

  
  

  “No!” Harry shouted, and though he had raised his wand no spell occurred to him. “No! It wasn’t us! We didn’t kill you-”
  On the word kill, the figure exploded in a great cloud of dust...
  _{(Deathly Hallows, Chapter 9, A Place to Hide).}

  
  
  

  
  

In what way do these charms actually protect Grimmauld Place? Was their intent to stop Snape from entering in the first place? Or just to stop him re-entering if he wanted to come back?

The Tongue-Tying Curse clearly does not protect the Fidelius Charm in any meaningful way. It would only silence Snape once he had already come back to Grimmauld Place, having already revealed the location to anyone he wanted. He could've entered accompanied by Voldemort and 40 Death Eaters and no-one could've stopped him.

The second element is even weaker. Was Moody's best hope really to rely on remorse?!? He believes that Snape is a heinous traitor and a cold-blooded killer. If he had it in his heart to kill Dumbledore in the first place why would he be remotely troubled by the dusty replica? As Harry wonders:

Had it worked, Harry wondered, or had Snape already blasted the horror-figure aside as casually as he had killed the real Dumbledore?
_{(Deathly Hallows, Chapter 9, A Place to Hide).}

Collectively, these defences just seem really poor and ineffective for an ex-Auror of Moody's talent and ability. Clearly they weren't effective in keeping Snape out since he re-entered the house that summer. Which means that either the defences weren't intended to keep Snape out or that they just weren't very good.

Did Moody think that his defences would be effective in keeping Snape out of Grimmauld Place? What was the point of them?

Answer

No

First, it’s important to note that Moody was not sure that his defenses would be proof against Snape. In the very quote given in the question:

We hope they’ll be strong enough both to keep him out and to bind his tongue if he tries to talk about the place, but we can’t be sure. It would have been insane to keep using the place as headquarters now that its protection has become so shaky.”

_{Harry Potter and the Deathly Hallows}

They knew that there was no guarantee that the spells would prevent Snape from either talking or entering. They had to do their best (obviously), so as to retain the house as an emergency resource and prevent Snape from taking advantage of it and anything it contained, but neither Moody nor the rest of the order was certain that they could keep the place safe. And indeed, Snape was able to defeat the protections, though he may have been aided by information he received from Mundungus.

That said, the protection is likely stronger than the question assumes (and certainly not without purpose).

• There was almost certainly nothing that the Order could do had Snape chosen to reveal the location of Grimmauld Place before returning there himself. They could only prepare for the situation in which Snape personally went to Grimmauld Place before revealing the location. For that particular situation, the Tongue-Tying Curse (and possibly others) would presumably prevent him from revealing the information thereafter.


• There’s no reason to believe that the dust figure of Dumbledore is merely meant to frighten Snape, or to play upon his feelings of guilt or remorse. Sure, Harry speculated that it was “just something to scare Snape,” and that Snape could have “blasted the horror-figure aside as casually as he had killed the real Dumbledore,” but we have no reason to think he understands what the spell really is. On the contrary, that, say Lupin, takes the time to dispel it suggests that it is probably a real threat.


• 
  

  There’s no reason to think that the figure vanishes when you say the word “killed.” Again, Lupin took the trouble of saying that he had not killed Dumbledore. At the very least, I suspect the whole statement is necessary:

  
  

  
  

  The intruder took a step forward, and Moody’s voice asked, “Severus Snape?” Then the dust figure rose from the end of the hall and rushed him, raising its dead hand.

  
  

  “It was not I who killed you, Albus,” said a quiet voice.

  
  

  _{Harry Potter and the Deathly Hallows}

  
  
  

  
  

  It is of course entirely possible that dispelling the dust figure requires both the statement of not having killed Dumbledore, and not actually having killed Dumbledore.

  
  


• 
  

  We don’t know for sure that the Tongue-Tying curse and the dust figure are the only protections on the house. There may have been others that were not noticed because Harry and company simply were not Snape.