I tried creating a way to stop people from damaging dog armor on people dogs using a claim plugin called Grief Defender. I asked the plugin creator and he said 

"Spigot has not added any events that I see for Wolf Armor.
 
{{if (this.count == 1 && entityliving instanceof EntityHuman)

{ org.bukkit.craftbukkit.event.CraftEventFactory.callPlayerItemBreakEvent((EntityHuman) entityliving, this); }

}}They only call the item damage/break events for player"
Right now there is no way to protect dog armor from being damaged using any plugin from my understand without this event.