While Dumrod executes his next move, Angus's group creates the rune barrier on Porky to protect themselves from the radiation. The barrier rune is very complicated but also fragile. This is also why Elder Forgus couldn't apply it to everyone.
If the dwarves or Angus's group launch a strong move, it may break the entire barrier. However, it is a different case for Porky. The giant pig has a larger body that can hide or protect the rune easily.
Unlike dwarf and human bodies, where the rune core is closely located in a small area, Porky's large body makes it easier to hide or overlap with other stronger barrier enchantments.
As long as this barrier core is not directly hit, it will not get destroyed, even if Porky makes a rough movement and goes toward the battlefield. Therefore, Angus and Elder Forgus prefer to make barrier runes on Porky.