agreed ... it's a bit lame to build things to protect your pets and see some alpha thing poping inside an killing everything...
I've just lots 5 bears a wolf and an elephant because of an alpha giant snake and it's very depressing to see a lots of effort vanishing this way :(
Army of the damned or regular mobs can be managed if you let your pet in neutral but an alpha ... even an alpha cow could kill every tamed pet