Cheaper than firearms I would say
From the New York Times of 1.15.15
A middle school principal wants to stockpile cans of corn and peas in classrooms for students to hurl at possible intruders as a last defense. In a letter Friday, Priscella Holley, principal at W. F. Burns Middle School in Valley, Chambers County, asked parents to have each student bring an eight-ounce canned item. The can “could stun the intruder or even knock him out until the police arrive,” Ms. Holley wrote. “The canned food item will give the students a sense of empowerment to protect themselves and will make them feel secure.” The school superintendent said the request had brought few complaints.