C#

class MyClass
{
     private readonly object locker;
     private String strToProtect;

     public String StringToProtect
     {
          get 
          {
               lock(locker) { return strToProtect; } 
          }
          set
          {
               lock(locker) { strToProtect = value; }
          }
     }

     private int anotherPrivateObject;

     public void ThreadFunction()
     {
          anotherPrivateObject = 0;   
          for(int i = 0; i < 10; i++)
          {
               anotherPrivateObject++;
               System.Threading.Thread.Sleep(100);
               System.Diagnostics.Trace(StringToProtect);
          }
     }
}
...
Main()
{
     MyClass instanceObject = new MyClass();
     instanceObject.StringToProtect = "set the string on this instance of MyClass";

     Thread myThread = new Thread(new ThreadStart(instanceObject.ThreadFunction));
     myThread.Start();

     instanceObject.StringToProtect = "changing this string should not be a problem";

     ...
}