You can also use cards that destroy all cards on the field such as Torrential Tribute, Dark Hole, and other trap cards that would prevent this monster from leaving the field. At this time all cards would be destroyed, but only this card will remain on the field, even if "Necrovalley" was destroyed. Therefore, no traps, spells/magic cards, and monster effects will be able to remove him off the field.
Because this card is unaffected by all card effects except its own, it will not gain the attack boost from "Necrovalley".
This card works well with Malefic monsters, as it is immune to their effects while "Necrovalley" is on the field and can attack alongside them.