Think I'll get padlocks for the goatyard gates. A year or two back a local publican who had a few animals as a bit of an attraction for customers got up one morning to find his billy goat gone but a lot of blood on the ground. The sort of quantity you get when you slit an animal's throat. He got rid of all his animals so there was no risk to the others.
I think 12 foot fences would be a good deterrent though. I've never seen fences that big.