FF, many of these Texas ranches given to commercial trophy-rack hunting are four- or five- on up to over 20,000 acres. High fence is very expensive. the owners don't high-fence small pieces. The primary purpose of the high fence is to keep deer out, not in, since a lot of effort goes into not having more deer than the carrying capacity of the land will allow. Also consider the effort gone into in order that the buck-doe ratio is biologically sound.
These ranches have a lot of habitat enhancement efforts made on them. Brush clearing (partial), restoration of native plants, and water supply, among other efforts. There is commonly a use of mineral supplements as advised by wildlife biologists. So, to deer from neighboring, unimproved habitat, it's Smorgasbord! time--and you wind up with too many deer, which is bad for the habitat.
So, high fence.
Shifting emphasis--and terrain/vegetation: The State of Michigan once high-fenced a 100-acre, heavily-wooded tract. This was maybe 40 years ago. It was known that there were over fifty deer within this tract. Hunters were allowed to try their luck (I don't recall the number of hunters at any one time.) The success rate was near zero. Size of tract, as such, is not necessarily the criterion.
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