Many of these places do pen the animals in small areas. They are used to humans and do not associate them with danger. They're fed on a schedule and the animals will make a pass by the "hunter's" location on a nearly pre-determined schedule. They're like pretty cows that have been conditioned to do a predictable routine.
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You shouldnt believe everything you read or hear. Im not going to pretend that places dont run hunts like this but there are more that dont and the deer are more free range than penned pets