For zoos, how to keep the visitors separated from the wild animals is an evolving science of its own, with the goal being to protect people even if they find their way past the primary barrier.
On Monday, president of the Pittsburgh Zoo and PPG Aquarium said the zoo where a 2-year-old boy was fatally mauled by African wild dogs over the weekend met or exceeded all safety standards for animals and visitors. Zoo president Barbara Baker said the tragedy is proof that no exhibit is "fail-proof."
The boy's mother had put him on a wooden railing at the edge of a viewing deck before he fell late Sunday morning. He bounced out of netting below before dropping more than 10 feet into the dogs' enclosure.
African wild dogs, also known as painted wolves, are social animals and skilled hunters. And if visitors come to a zoo with a well-designed habitat, it's almost like seeing them in the wild.
"A habitat like this gives an idea how wild dogs live," said John Lewis, LA Zoo director.
Lewis said many considerations go into habitat design, but the crux is safety.
Whether a better barrier system could have prevented the Pittsburgh tragedy will be the subject of investigation, but over the decades, zoos have moved increasingly to multiple barrier systems, like ones at the LA Zoo.
In recent years at the LA Zoo, an orangutan and a chimp have managed to escape their enclosures briefly, but there were no injuries.
"Big part of our business is protecting the public but also the animals as well," Lewis said.
Older habitats often relied on being at a lower level than the viewing point, but that tended to tempt people to peer over the barrier, so that type of design has fallen out of favor.
Associated Press contributed to this report.