How can I get a Grid to draw Borders for blank cells?

I have an ItemsControl which uses a Grid as the ItemsPanelTemplate, and sets the Grid.Column and Grid.Row on the ItemContainerStyle to position data items in the grid

Is there a way to either add GridLines to the Grid, or to fill in the blank cells with a Border?

Right now I have ShowGridLines set to True which makes the dotted lines, however I want Horizontal lines to show up, and I'd prefer solid GridLines

There is a rather large amount of XAML, but here's a screenshot of how my XAML is laid out:

Sorry, styling the grid lines can't be done. Atleast not in an easy way. See the following question for an explanation: How can I change the color of the gridlines of a Grid in WPF?

MSDN docs say "Only dotted lines are available because this property is intended as a design tool to debug layout problems and is not intended for use in production quality code. If you want lines inside a Grid, style the elements within the Grid to have borders."

Edit: If you want the borders you can create a custom Grid and draw the GridLines in OnRender method of the control.

    using System.Windows;
    using System.Windows.Controls;
    using System.Windows.Media;

    namespace BorderGridControl
    {
        public class GridControl : Grid
        {
            #region Properties
            public bool ShowCustomGridLines
            {
                get { return (bool)GetValue(ShowCustomGridLinesProperty); }
                set { SetValue(ShowCustomGridLinesProperty, value); }
            }

            public static readonly DependencyProperty ShowCustomGridLinesProperty =
                DependencyProperty.Register("ShowCustomGridLines", typeof(bool), typeof(GridControl), new UIPropertyMetadata(false));

            
            public Brush GridLineBrush
            {
                get { return (Brush)GetValue(GridLineBrushProperty); }
                set { SetValue(GridLineBrushProperty, value); }
            }

            public static readonly DependencyProperty GridLineBrushProperty =
                DependencyProperty.Register("GridLineBrush", typeof(Brush), typeof(GridControl), new UIPropertyMetadata(Brushes.Black));

            public double GridLineThickness
            {
                get { return (double)GetValue(GridLineThicknessProperty); }
                set { SetValue(GridLineThicknessProperty, value); }
            }

            public static readonly DependencyProperty GridLineThicknessProperty =
                DependencyProperty.Register("GridLineThickness", typeof(double), typeof(GridControl), new UIPropertyMetadata(1.0));
            #endregion

            protected override void OnRender(DrawingContext dc)
            {
                if (ShowCustomGridLines)
                {
                    foreach (var rowDefinition in RowDefinitions)
                    {
                        dc.DrawLine(new Pen(GridLineBrush, GridLineThickness), new Point(0, rowDefinition.Offset), new Point(ActualWidth, rowDefinition.Offset));
                    }

                    foreach (var columnDefinition in ColumnDefinitions)
                    {
                        dc.DrawLine(new Pen(GridLineBrush, GridLineThickness), new Point(columnDefinition.Offset, 0), new Point(columnDefinition.Offset, ActualHeight));
                    }
                    dc.DrawRectangle(Brushes.Transparent, new Pen(GridLineBrush, GridLineThickness), new Rect(0, 0, ActualWidth, ActualHeight));
                }
                base.OnRender(dc);
            }
            static GridControl()
            {
                DefaultStyleKeyProperty.OverrideMetadata(typeof(GridControl), new FrameworkPropertyMetadata(typeof(GridControl)));
            }
        }
    }

I Tried it out and it seems to be working great.

Here an example of using:

    <controls:GridControl ShowCustomGridLines="True"
                          GridLineBrush="Red"
                          GridLineThickness="1">
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
    </controls:GridControl>