cordon off
To restrict access to a particular area by using a rope, tape, or other means. A noun or pronoun can be used between "cordon" and "off." That section of the restaurant has been cordoned off for a private party.
cordon something off
to mark off an area where people should not go with a rope, tape, ribbon, etc. The police cordoned the scene of the crime off, and we could not even get close. They cordoned off the area.