WPF - Align checkbox with datagrid column - wpf

Question

I need to position a checkbox above a column in a datagrid, and keep the checkbox aligned with the left edge of the column, even if the columns are resized (or reordered) by the user.
Putting the checkbox in the column header is probably not an option.
The first challenge is knowing when the user is resizing a column.
There is a ColumnHeaderDragStarted event, but I think that is raised when the user drags a column header to reorder it. Does it also apply to a column resize operation?
The next challenge is re-positioning the checkbox as the column is moved. How can the position of the left edge of the column ("Val1", for example) be determined w/r/t to the left edge of the containing grid? I suspect that if that value can be determined, it can be used to position the checkbox.
Thanks for any insights in to this problem --
UPDATE 2
This xaml is providing much of the desired behavior, but the alignment isn't right. If the user move the separator between "Id" and "Val1", the checkbox moves.
The goal, however, is to have the checkbox remain aligned above "Id"; it should move only when the separator between "Name" and "Id" is moved.
<Grid x:Name="LayoutRoot">
<Grid.RowDefinitions>
<RowDefinition Height="32" />
<RowDefinition />
</Grid.RowDefinitions>
<DataGrid x:Name="DataGrid"
Grid.Row="1" Grid.Column="0" />
<Canvas Grid.Row="0" Grid.RowSpan="2" >
<CheckBox Content="Check One"
Canvas.Top="10"
Canvas.Left="{Binding Columns[1].ActualWidth, ElementName=DataGrid}" />
</Canvas
</Grid>
UPDATE:
This seems like it might be a useful approach:
https://stackoverflow.com/a/41094009/107037
The challenge of positioning the checkbox still exists, however...
Since someone asked:
Grid x:Name="LayoutRoot">
<Grid.RowDefinitions>
<RowDefinition Height="32" />
<RowDefinition />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<CheckBox Content="Check One" Grid.Column="1" />
<CheckBox Content="Check One" Grid.Column="2" />
<DataGrid x:Name="DataGrid"
Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="4" ></DataGrid>
</Grid>