After protests turned violent at several college campuses in recent months, some colleges and universities are wondering if they'll be next.

Some campus police are trying new tactics to try to keep events peaceful. Other schools have abruptly canceled controversial speakers over safety concerns, as the University of California, Berkeley, did with conservative writer Ann Coulter.

Police from about 40 schools took part in protest preparation and response trainings in March in California, Indiana and Maryland. Another session takes place Thursday at the University of Hartford in Connecticut.

At Vermont's Middlebury College in March, protesters shouted down a guest speaker. A professor was injured in a melee afterward.

The previous month at Berkeley, three people were arrested in a protest that stopped a speech of a right-wing commentator. Six people were injured.