In the 16th century A.D. the Magistrate of East Hampton in Eastern North America, which formed following European colonization, called for an annual witch hunt, in which wizards and witch hunters from all over the world congregate to hunt witches.
It is rumored that on this year's hunt, there will be a lunar eclipse on the super Blood Moon, which will last 9 minutes. During this time, thousands of unicorns will emerge from the woods to mate. The witches, who long for immortality, will seek the rarest of the unicorn, the Ethereal Azure Horn.
It is a rare mutation among the unicorns, and only a handful have been spotted throughout history. It has been said that any human to have their heart pierced by the Ethereal Azure Horn shall gain immortality. However, only a virgin whose heart is filled with extreme grief and sorrow can touch the horn. The worst part is that any dead unicorn will turn into a vengeful, bloodthirsty zombie centaur that cannot be subdued by any conventional means.
The magistrates, while aware of the threat of dead unicorns, want to seize this opportunity to round up all the witches. They also want to put up perimeters around the woods to prevent the likes of commoners from getting involved - only hunters should be able to get in and out.
The witches can transform into werewolves upon nightfall and gain immerse strength. They can detect presence of magic within miles.
The unicorns must remain fantasy creatures at all costs
The perimeter must prevent entry to commoners (muggers/no-mags)
How can the magistrates build a perimeter that only keeps out non-magic humans, that also doesn't look like a trap to the witches?