In some cases, these activities may require design or engineering elements; the rigging of scaffolding for a particular purpose, calculations to support trenching/shoring activities, or engineering associated with tower crane bases are just a few examples of such "means and methods." Means and methods of construction are ordinarily understood to be covered under general liability (GL) policies, but the lack of coverage for economic damages makes insuring this professional risk under a GL policy only semi-effective. Contractors can obtain broader coverage for these activities by purchasing contractors professional liability insurance.