Photograph by “AnRo0002.”
From the Wikipedia article on Trifoliate Orange (Citrus trifoliata or Poncirus trifoliata):
The cultivar “Flying Dragon” is dwarfed in size and has highly twisted, contorted stems. It makes an excellent barrier hedge due to its density and strong curved thorns. Such hedges have been grown for over 50 years at Oklahoma State University in Stillwater, and are highly student-proof.
Now you know what to do. Surround your university with a hedge of the Flying Dragon cultivar of Citrus trifoliata, and your problems are solved. As long as you put up the hedge when the students are out, not when they are in.