Can't get underline to show up when triggered - wpf

Question

I have the following style, but when the mouse over trigger is true, no underline shows up on the text.
<Style x:Key="HyperlinkToggleButtonStyle" TargetType="ToggleButton">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<TextBlock x:Name="TextBlock">
<ContentPresenter Content="{TemplateBinding Content}" ContentTemplate="{TemplateBinding ContentTemplate}"/>
</TextBlock>
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="false">
<Setter Property="Background" Value="{StaticResource StandardBackground}"/>
<Setter Property="Foreground" Value="Black" />
<Setter Property="FontSize" Value="12"/>
<Setter Property="FontStyle" Value="Normal"/>
<Setter Property="FontWeight" Value="Normal"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="true">
<Setter Property="Background" Value="{StaticResource StandardBackground}"/>
<Setter Property="Foreground" Value="{StaticResource StandardBlue}" />
<Setter Property="Cursor" Value="Hand" />
<Setter Property="FontSize" Value="12"/>
<Setter Property="FontStyle" Value="Normal"/>
<Setter Property="FontWeight" Value="Normal"/>
<Setter Property="TextBlock.TextDecorations" Value="Underline"/>
</Trigger>
</Style.Triggers>
</Style>

Answer 1

This might not be an ideal solution, but you could define the trigger in your control template. Don't forget to reference your TextBlock with the TargetName property on the setter.
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<TextBlock x:Name="TextBlock">
<ContentPresenter Content="{TemplateBinding Content}" ContentTemplate="{TemplateBinding ContentTemplate}"/>
</TextBlock>
<ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="true">
<Setter TargetName="TextBlock" Property="TextBlock.TextDecorations" Value="Underline"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>

Answer 2

The TextDecorations property is not inherited so setting the value on the Button (which is what your trigger is targeting), will not accomplish what you want. You can probably use a StoryBoard to do that, but I can't remember if a storyboard can target an element defined in a template (only way to find out is to do it).