Last Christmas, a tiger broke free from its enclosure at San Francisco's zoo, killing one teenager and injuring two others. Dickerson Park Zoo’s staff is trying to prevent a similar attack here. Its changes are designed to protect the thousands of people who come to the zoo while still allowing visitors to get an up-close look at the animals.

To any youngster's eager eyes, a lion looks more docile than dangerous. But there's no mistaking just how deadly lions and other large predators are, even when they’re confined.

"We've actually increased the height of the barriers around the exhibit itself,” said zoo Superintendent Mike Crocker.

Four feet have been added to the fence around the lions, making the lowest point stand 15.5 feet high, and there have also been changes at the viewing area. Visitors used to be able to peer over a rock formation to look at the lions. Now cables have been added and, above that, even more fencing.

Crocker says it's designed to not only keep lions inside the walls but also spectators outside the barriers. He says, on rare occasions, parents have dangled their kids over the old wall.

"A lion actually came after them and jumped up and actually slapped a child down on the bottom of their shoe,” said Crocker.

The new configuration allows a camera to poke through for those great snapshots but that's about it.

Electric cables are also along the rock barrier inside the perimeter and again at the top of the fence. It won't hurt the animals but it would likely stop them from escaping and causing any harm.

"Safety is a very high priority," said Crocker.

Renovations are also taking place at the bear exhibit. The original barrier had wood poles that begin to rot, so they're being replaced with steel frames.