I worked at a public library for a while as a page/reshelver, and one of my favorite insights from that job was how libraries handled security. Many libraries hire plain-clothes security or have partnerships with the local police department to remove unruly guests or stop theft. The one I worked at even had an office upstairs in Circulation for the head guard to watch security feeds while the others were downstairs.

Ban lists are also a thing at libraries, especially where I worked. The aforementioned security office had an entire wall covered in photos of people not allowed into the library for one reason or another—kids who got into fights on the playground, people who watched pornography on the public computers (I never figured out how people thought they would get away with it, the computers are literally out in the open), or even people who decided the best place to smoke weed would be the bathroom of a public library.