Saphira

A moment passed as Eragon reflected on what Oromis had told him. “These wards, do they only drain energy from you when they are activated?”

“Aye.”

“Then, given enough time, you could acquire countless layers of wards. You could make yourself . . .” He struggled with the ancient language as he attempted to express himself. “. . . untouchable? . . . impregnable? . . . impregnable to any assault, magical or physical.”

“Wards,” said Oromis, “rely upon the strength of your body. If that strength is exceeded, you die. No matter how many wards you have, you will only be able to block attacks so long as your body can sustain the output of energy.”

Eldest, Chapter: the nature of evil