Other forms: cordons off
To cordon off is to block an area, usually with a rope, so that people are kept from going there. After a falling tree crashes through the front window of a cafe, police might cordon off the entrance until repairs are made.
When you cordon something off, you restrict access to it. Following one too many accidents on the playground, a school may cordon off the climbing structure entirely. Your sister might decide to cordon off her treehouse ladder with a rope if she's fighting with her friends. The verb cordon originally meant "ornament with a ribbon," from cordon, "cord," and also "line of troops guarding a place."