What was Dumbledore's extra protection on the school?

[vmonte]

No: HPFGUIDX 137088

Geoff:
...A few weeks ago, I referred to a Biblical example in the
case of St. Paul, who as Saul of Tarsus, set out to crush the early
church and was not too fussy about the methods he used such as
imprisonment and killing. He was at the stoning of Stephen, not as
one of the perpetrators but egging them on from the side. Then the
Bible narrative records that he met the risen Christ and, realising
the mistakes he had made, became a totally different man who went on
to be possibly the finest worker for Christ of his generation. And
there are modern day parallels within the church.

vmonte:
This is interesting Geoff. I actually think that if JKR was to use 
St. Paul's story it would make more sense to use it for Snape. I do 
not think that Snape has yet made a "spiritual" conversion to the 
good side. I believe (I know that most of you don't) that Snape is 
just too ruthless a character to have had any kind of "aha" moment-- 
yet. 

I do think however, that his anger at Harry for calling him a coward 
(at the end of HBP) might be suggestive of someone who is 
unconsciously feeling guilt for what he has done. I think that 
Dumbledore is the only person that loved, trusted, and respected 
Snape--ever. And I think that this is going to start to eat away at 
Snape. 

I could see Snape freaking out if he were to see some kind of 
resurrected form of Dumbledore (in the love room perhaps?) or... 

I keep thinking of the Draught of the Living Death potion that was SO 
ready and available at the school. That potion could SO easily have 
been used to avoid killing Dumbledore at the end of HBP. 

If Dumbledore knew what Draco's mission was about why wasn't he 
prepared? Why does he tell Harry that he has made other precautions 
to protect the students at the school? What were they? Was the 
precaution something to do with protecting Draco? (Aside from the 
assisted suicide theory.) 

I think that Dumbledore was genuinely surprised that Draco was able 
to get people into the school, so I'm thinking that DD's extra 
precautions were more about Draco's task. (I also think that 
Dumbledore was not expecting Snape to do what he did. He seemed so 
tragically stunned by Snape--very sad.)  

Did Dumbledore have an alternate plan involving Slughorn?  

The reason why the unused Draught potion bothers me so much is that 
in every book the kids ALWAYS use all the creatures, items, lessons 
and spells learned to save themselves or others. That didn't happen 
in HBP. Why? 

So here are a few things that keep nagging at me...

1.What does Slughorn need with all that spider venom? 
  (Doesn't spider venom paralyze the victim?)

2. Wasn't there also vat of polyjuice somewhere? 

3. And why wasn't the Draught potion used?

The ability to paralyze, disguise, and fake a death...NOT USED???? 
WHY!!!  

Vivian