To Create a Named Boundary from Active Fence

Select the Place Fence tool ( Drawing > Home > Selection > Fence Tools split button).
In the tool settings window, set the Fence Type and Fence Mode.
Place a fence.
In the tool settings, click the Expand arrow.
Click the Create Named Boundary from Active Fence icon.

An untitled named boundary is added to the list box.
In the list box, enter a name for the new named boundary.
(Optional) In the Description column, right-click and enter a description.