Thanks Richard. I was having the same problem and that article helped.
Essentially, this is a pretty minimal generic setup.
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<Label Content="(0,0)" Grid.Row="0" Background="Yellow"/>
<Label Content="(1,0)" Grid.Row="1" Background="LightBlue" />
<Label Content="(0,1)" Grid.Row="0" Grid.Column="1" Background="MediumPurple" />
<Label Content="(1,1)" Grid.Row="1" Grid.Column="1" Background="Green" />
<GridSplitter Grid.Row="0"
Height="10"
Grid.ColumnSpan="2"
HorizontalAlignment="Stretch"
VerticalAlignment="Bottom" />
</Grid>