internal GeometryGroup CurrentGeometry
        {
            get { return (GeometryGroup)GetValue(CurrentGeometryProperty); }
            set { SetValue(CurrentGeometryProperty, value); }
        }
        internal static readonly DependencyProperty CurrentGeometryProperty =
            DependencyProperty.Register(
            "CurrentGeometry",
            typeof(GeometryGroup),
            typeof(ShapeEditorControl),
              new FrameworkPropertyMetadata(default(GeometryGroup), CurrentGeometryChanged));

public void RemoveDependency()
        {
            DependencyProperty prop = CurrentGeometryProperty;
            var registeredPropertyField = typeof(DependencyProperty).
              GetField("RegisteredPropertyList", BindingFlags.NonPublic | BindingFlags.Static);
            object list = registeredPropertyField.GetValue(null);
            var genericMeth = list.GetType().GetMethod("Remove");
            try
            {
                genericMeth.Invoke(list, new[] { prop });
            }
            catch (TargetInvocationException)
            {
                Console.WriteLine("Does not exist in list");
            }

            var propertyFromNameField = typeof(DependencyProperty).
              GetField("PropertyFromName", BindingFlags.NonPublic | BindingFlags.Static);
            var propertyFromName = (Hashtable)propertyFromNameField.GetValue(null);

            object keyToRemove = null;
            foreach (DictionaryEntry item in propertyFromName)
            {
                if (item.Value == prop)
                    keyToRemove = item.Key;
            }
            if (keyToRemove != null)
                propertyFromName.Remove(keyToRemove);
        }