It's a topic that can and will be debated around campfires -both real and virtual- endlessly.
I suppose for me it depends on the animal and the terrain and the area fenced. If the animals in question would estblish their natural range well within the area fenced in, then it is really academic at that point. Fence or no fence, they'd live in that area until moved out my overpopulation, predation, or search for food/water during drought.
Something that gave me pause to think about all of this can while doing a buff hunt in Zambia in game concession in GMA. No fences and a large area to hunt. I asked my PH how difficult it was going to be to find a herd and he chuckled. On his concessions, they hid up in the shade in one of two places, watered in the river, and fed in between in the early morning and late afternoon. He said he knew where they would be, and he did. Also, it turned out the lions knew their habits too, which made for intereting times.
