Its not to keep out the natural predators. Its too keep the animal population we have in, to prevent them from being killed on roads and by neighboring hunters. Most if not all of the exotics on our property are also found free range, but not in the populations that we've been able to create by high fencing. The drawback is that without control some of the species do so well that they can overpopulate.
So basically you have two options, a) rarely, if ever, see an exotic or b) high fence and follow appropriate practices to manage the ecosystem. This is done with biologists that take animal counts and also inspect the property itself for signs of overpopulation. Basically they take all the factors into account and give you a report on the health of your ranch's wildlife and ecosystem. (edited to add
They also provide a count on each animal and also provide a goal count for your specific property. Sometimes you aren't to cull anything. Sometimes you are only supposed to cull doe, other times, just bucks, other times shoot everything that moves. Basically the owner becomes the natural predator since there aren't any. There are almost no natural predators of wild game in Texas. Coyotes have easier pickens with people's chickens, goats, calves. Mountain Lions are so rare because they've been killed off by the people with the goats, chickens, and cows.
One of the fringe benefits of high fencing and having a wonderful place to retreat, that's filled with a variety of wildlife, is the ability to fill your freezer with meat, educate children on wildlife and conservation, etc.
If all we wanted to do was shoot animals we wouldn't spend the money on high fencing, biologists, and ecosystem improvements such as building ponds, clearing the cedar (that is not native to texas). You'd just stick a feeder up and shoot every deer that walked by.
As a perfect example, every time we go up there we pick an area and cut all the cedars down in the area. By cutting all the cedars down you can turn a dry creekbed into a flowing stream. Cedars are the scourge of west texas. At one time, before cedars West Texas was nowhere NEAR as arid. I'll spend a lifetime cutting down cedars unfortunately.