Lots of definitions and opinions on this topic.
Some like Pope & Young Club say if the animal is enclosed behind game-proof fence, no matter the size of the tract, it is a canned, and therefore a non-fair-chase hunt. This would eliminate many intensively managed areas in Texas and almost all of South Africa (of course SA game isn't PY consideration.)
Others would try to define the acreage within such an enclosure and suggesting that a large enough enclosed acreage would negate the fence.
This is the litmus test I use. If you are within an enclosure, no matter the size, and the animal you kill is recovered near the fence, will pictures of the kill be organized to hide (deny) the fence? If so, that says a lot about what the hunter really believes about
his "accomplishment".