Everyone is replying to my comment to talk about social nets and failures in the justice system, but I agree that the math is a more interesting challenge. The site I was talking about is thousands of acres in an undeveloped area, and while you accurately note the barrier is more cost effective, the number of patrols and response time for incidents (including false alarms) grows with scale. The owner could lock down the site like a fortress from a James Bond movie, but let's not forget that those thousands of acres are just gathering sunlight, so at some point it stops being cost-effective.

And I mostly introduce this issue as a contrast to panels on developed land like the canals, which serve other functions and are less likely to have the risks associated with such a single-purpose site.