BadMedicine, sheep and goat fence is four-foot high mesh wire, with one or more strands of barbed wire on top. The crossings are underneath, where the hogs have rooted out a little washed-out spot. I have even seen deer use them.
One year on our deer lease, a trapper caught a young four-point in a snare at one of these "crawl-unders". A buddy of mine and I tied the deer's feet, undid him from the snare, tossed him in the back of the truck, and hauled him to camp. "Well, whadja find?", someone asked. "A little buck." "Where is he?" "Right here," I said as I undid the calf-roping-style clove hitch and let the deer leap into the group...Deer camp is fun!