There is an area of my land which has been used to graze cows for many years. It is only fenced on three sides, because the fourth side is a wooded mountain, and cows will not wander away with that on one side. I want to turn that into my male goat pasture. Will I need to fence in the fourth side? I don't care if the goats go up the mountain, but up and over is a national forest where they should not go.