In a UI I'm building, I want to adorn a panel whenever one of the controls in the panel has the focus. So I handle the IsKeyboardFocusWithinChanged event, and add an adorner to the element when it gains the focus and remove the adorner when it loses focus. This seems to work OK.

The problem I'm having is that the adorner isn't getting re-rendered if the bounds of the adorned element changes. For instance, in this simple case:

<WrapPanel Orientation="Horizontal"
           IsKeyboardFocusChanged="Panel_IsKeyboardFocusChanged">
   <Label>Caption</Label>
   <TextBox>Data</TextBox>
</WrapPanel>

the adorner correctly decorates the bounds of the WrapPanel when the TextBox receives the focus, but as I type in text, the TextBox expands underneath the edge of the adorner. Of course as soon as I do anything that forces the adorner to render, like ALT-TAB out of the application or give another panel the focus, it corrects itself. But how can I get it to re-render when the bounds of the adorned element change?