You might be able to achieve this by using a style in a global scope (e.g. your App.xaml file):
<Application.Resources>
<Style TargetType="{x:Type StackPanel}">
<Setter Property="KeyboardNavigation.IsTabStop" Value="False" />
</Style>
</Application.Resources>
Then this way any StackPanel
in your application won't be a tab stop.