[Peacekeeper]

Another way to protect your summoning commander is to research the level 2(i think) enchantment spell (returning is in the name somewhere). Have him cast it the first round of combat(since hes getting attacked, that means this gets cast first) and whenever he gets hit he will return safely to your home city...which happens to be where he is anyway. At the cost of 1 astral pearl per combat, you will never lose your commander to being attacked by void summons.