public bool Locked {get; set;}

// The Locked property is displayed in the TOC as a lock symbol next
// to each element.  If locked the element can't be selected in the layout
// using the graphic selection tools.

//Perform on the worker thread
QueuedTask.Run(() =>
{
  // Reference and load the layout associated with the layout item
  Layout layout = layoutItem.GetLayout();
  if (layout != null)
  {
    //Reference an element by name
    Element element = layout.FindElement("MyElement");
    if (element != null)
    {
      // Modify the Locked property via the CIM
      CIMElement CIMElement = element.GetDefinition() as CIMElement;
      CIMElement.Locked = true;
      element.SetDefinition(CIMElement);
    }
  }
});