Unfortunately, unless we catch the person in the act and they don't affect your blocks or build bridges, there's really nothing we can do. It is the animals' owner's responsibility to protect them by setting up barriers to keep other players and creatures out. A double ring of high fence or a fully enclosed building is what you need, plus a precious stone covering the whole area to prevent breakins, mining under or bridging over. If a griefer gets into your house somehow and we can see that they did break in, we will punish them, but we will not replace your animals because the server does not log what animals you had or were killed, and we cannot just give animals away on the word of a player.
