I guess the primary aspect is whether the animal has a "fair chase" chance to evade the hunter. And, of course, is wild enough to want to.
"Proper" size of a fenced tract is a function of the type of vegetation. For instance, the state of Michigan's wildlife agency once built a deer-proof fence around a 100-acre tract of heavy timber/underbrush. They knew that at least 100 deer were within the fence. The number of hunters allowed in during the season was controlled, but tens of hunter-days accumulated. Three deer were taken. Most hunters reported seeing no deer at all.
To me, then, each piece of property is a different case. If the tract mentioned in the other thread is buffalo-proof fenced, it sounds on the edge of "unfair"--but if it's broken ground and mostly covered with thick brush it might be okay. Sounds small, though.
Regardless, fair-chase morals and ethics apply, which includes a challenge to the hunter. If there is no challenge, it's not hunting. It's merely butchery.
So count me in with Slick...
Regards,
Art