I have 12 acres, with several fields to rotate them in. The main fence next to the barn is 6 feet high with woven wire on cedar posts. I was days away from getting a portable solar electric fence of this type:
I was going to use this to rotate them in the other fields. I was going to get two ewes and one ram. So technically at times I would have to separate them to keep them from having early pregnancies. That would leave them down to two. I was going to get a border collie to protect them but discovered that they actually have a predator/prey relationship and would not serve to calm them down any but further the fear.
I also have about 20 chickens as well.