i dont know if any of you remember but in a previous discussion on this topic i stated my idea as a horcrux would be hogwarts itself, it fits all the criteria and it would never ever be suspected to be one. the only analogy the best place to hide something is in right out in the open, by making hogwarts a horcrux well its protected by DD the most powerfull wizard int he world. not only that who in there right mind would distroy hogwarts, or would want to distroy it, unless they knew that it was a horcux. a funny line comes to mind, you;d have to be insane to make hogwards a horcrux, well voldemort isnt insane. along with all this hogwarts fits other the criteria for a horcrux. - not only is it related to all 4 of the great founders, its the culmination of there efforts, what would be more symbolic of power( that which voldemort craves the most) along with fame, then put your soul into hogwarts, and for all intense purposes puting yourself on the same level as the four founders.
- hogwarts is something that voldemort loves, he love the castle more then anything, it was his only true home, thus says DD, and so it would just makes sense in someway that voldemort would want to mark his home with his soul.

Could you imagine the pain and sorrow Harry would feel if he had to destroy Hogwarts to kill Voldemort.

Also Hogwarts has been the only true home Harry has ever known just like Voldemort. Isn't it amazing how Voldemort and Harry's past and feelings mirror each other.