WPF Clip Rectangle

I have a UserControl that is 45x45 (hardcoded size - it's part of a grid of items). When a certain property has a value I want to show a "clip" in the upper right-hand corner indicating this. The visibility itself is easy to accomplish, however my Rectangle goes outside the bounds of the control and overlaps on other controls. I tried using the "ClipToBounds" property, but it didn't do anything. When I added that to the overall control the clip wo开发者_StackOverflow社区rked perfectly but my hover effects on the main rectangle (fills the cell) stopped working.

Any ideas? I'm confident this is simple to do, but still being pretty new to WPF (and horrible at geometry - hence not using the Polygon) I'm a bit lost.

Here is the full markup:

<Grid>        
    <Rectangle x:Name="MainRectangle" Fill="{Binding Background}" Opacity="0" MouseEnter="MainRectangle_MouseEnter" MouseLeave="MainRectangle_MouseLeave">
        <Rectangle.Triggers>
            <EventTrigger RoutedEvent="Rectangle.MouseEnter">
                <BeginStoryboard>
                    <Storyboard>
                        <DoubleAnimation Storyboard.TargetProperty="Opacity" From="0.0" To="0.8" Duration="0:0:0.33" AutoReverse="False" />
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger>
            <EventTrigger RoutedEvent="Rectangle.MouseLeave">
                <BeginStoryboard>
                    <Storyboard>
                        <DoubleAnimation Storyboard.TargetProperty="Opacity" From="0.8" To="0.0" Duration="0:0:0.33" AutoReverse="False" />
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger>
        </Rectangle.Triggers>
    </Rectangle>
    <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center" Text="{Binding VisualCount}" />
    <Rectangle Fill="Black" HorizontalAlignment="Right" Height="20" Margin="0,-14,-20,0" Stroke="Black" VerticalAlignment="Top" Width="20" Visibility="{Binding HasNotes}">
        <Rectangle.RenderTransform>
            <RotateTransform CenterX="0" CenterY="0" Angle="45" />
        </Rectangle.RenderTransform>
    </Rectangle>
</Grid>

---

Here be a simple path:

<Path Fill="Black" HorizontalAlignment="Right" Visibility="{Binding HasNotes}">
    <Path.Data>
        <PathGeometry>
            <PathFigure StartPoint="0,0">
                <LineSegment Point="14,0"/>
                <LineSegment Point="14,14"/>
            </PathFigure>
        </PathGeometry>
    </Path.Data>
</Path>