Release the Polacanthus when they're ready and transport them into the small enclosure. Wait until you've released some of the dinosaurs into the first enclosure and have some guests back on the island. To get them as close as possible to the guests, build a small, concrete-fence enclosure between the Creation Lab and the Viewing Gallery (and close to all those unsuspecting guests.) Once they break out they need to trample a guest before they become content again. This means that there is essentially a timer. The problem here is that the dinosaurs will become agitated and panic when in an unsuitable enclosure, but once they are released or break out they comfort levels will return to acceptable levels. Simply releasing herbivores amongst guests won't do the trick, they need to be panicking. They they are one of the few with the highest comfort threshold for herbivores (60%). If you've followed the walkthrough to a tee, you won't have released this species yet. Incubate a pair of Polacanthus at the new Creation Lab. The setup is complicated and a little random and the achievement itself seems a little buggy. You need to photograph a Herbivore attacking a guest and it's a little trickier than you might expect. If you unlocked it way back on Isla Matanceros, release and immediately sell a single Polacanthus then skip ahead.
