Hogwarts protection spells

[rbookworm46]

No: HPFGUIDX 135639

David L.:
Hogwarts is known to be a vast store of magical energies, probably 
one of the reasons Voldemort wanted to teach in the school. I doubt 
that these energies just dissipate after every headmaster's death. 
Plus, as much as most of us are attached to old Dumbledore the guy 
was just a headmaster.  Just because he died doesn't mean Hogwarts 
will crumble too. The school is much bigger than any one person. 
There is a principle behind which the school stands for and that is 
much bigger than Dumbledore. So I think that the spells that protect 
the castle and its grounds will be around for a long time to come.


Bookworm:
(Scholastic HBP, Ch27, p583) 
"As they flew over the dark, twisting lane down which they had 
walked earlier, Harry heard, over the whistling of the night air in 
his ears, Dumbledore muttering in some strange language again.  He 
thought he understood why as he felt his broom shudder when they 
flew over the boundary wall into the grounds: Dumbledore was undoing 
the enchantments he himself had set around the castle so they could 
enter at speed."

I had a bunch of questions when I read this: 
What about the older protections?  Were they not strong enough to 
hold against Voldemort?  What were they, and what did Dumbledore 
add?  Did Dumbledore reset the protections after they crossed the 
boundary?

The last question concerns me the most, because I don't think he 
did.  How vulnerable is Hogwarts now with just the older protection 
spells?  A while ago, several of us had a debate on where the battle 
would be in book 6 and Jim argued that it would be at Hogwarts –
I owe you one, Jim :-)   

Does this mean the battle in book 7 will be someplace else?  Or if 
it will be easier for the DEs and Voldemort to enter Hogwarts, will 
there be an all-out battle with the cast of thousands?  After all, 
we haven't seen *all* of the Houses united yet.  Does Harry need
just a few from each House, or all the students at the school?

Ravenclaw Bookworm <who remembers JKR saying HBP starts answering 
more questions that it asks!>