He glanced around the room and thought, it was time to work in making runic weapons again and not only that, he would have to pretty much waste all the weapons he made in advance, since they could not be modified anymore, neither can they be sold in fear of being tampered with again by another runecaster.
From now on, his engraved weapon needs to have some backup functions that would smartly detect any sort of tampering attempt and block such attempts from affecting the rune itself. If the interference becomes too great, the rune would simply and without any violent reaction just dissolve.
