Over my dead (gorgeous) body.

[Eruanna]

This is an interesting question. I'm intrigued by Eomer's idea of the dead living somewhere else.
The spirits of dead elves (and men) go to the Halls of Mandos. Tolkien said that the elves, after a time, could be re-embodied and go to join their kin in Aman.
Perhaps from there, they are able to 'watch over' their graves on Middle Earth, as Arwen 'watched over' Aragorn, from afar?

[burrahobbit]

No. It doesn't have anything to do with that. Except folklore. Kind of.

[Eruanna]

You are nothing if not definite in your observations Burrahobbit! That's it? End of discussion?

narfforc said:

I think a lot of what Tolkien wrote about burial mounds comes from myth and folklore. The ancients worshiped such places as entrances to the underworld.

In Icelandic, Scandanavian, Celtic and Ancient British folklore (among others) there are also tales that have burial mounds being places where one could enter the Land of Faerie. Perhaps it is simply that Professor Tolkien was influenced by these ideas and tales when he wished to emphasise the tragic deaths of those interred in the mounds.
As far as I understand it, barrows and burial mounds are also said to be particularly strong in magnetic and or magical influence as they are often constructed at the meeting points of ley lines. I don't know much about ley lines and such, so I would not like to dismiss the idea out of hand.

[Keeper of Dol Guldur]

Nobody messed with the Barrow Downs, or the Paths of the Dead ... or the Mere of Dead Faces.

Why? They were haunted.

Now, while "fell spirits" are different from great warriors and lords who fell at their peak ... the idea that the dead are something to be respected and left alone still stand.

A grave is a holy place ...

And we all know vampires have a thing about holy ground ...

Nobody treaded on the "Death Down" at Helm's Deep either. People didn't want any nasty orc ghost cursing them maybe ... but more likely they just shuddered at the thought of going near a mass grave.

So ... 1 part respect for the dead, 1 part fear of supernatural, and 1 part genuine concern that your head could be the next one speared and put on display, and the power of these places is obvious.

[Saurreg]

I have read before that animals such as cats and dogs have a sense of awareness that is beyond ours and hence what they detect is not within our capability to comprehend. Perhaps there is some residual aura or potency in the remains of the dead which can only be percieved by such animals and make then uneasy? Orcs included of course.

As for those which do not partake in this gift, perhaps its the reputation of the dead and fear of the unknown that prevents them from entering what they percieve as a "haunted" forbidden ground. Imagine after all, runs wild.