Grid Xamarin.Forms

Hi,

I have a Grid on Xamarin.Forms and I want it to be on the bottom of every page on my app. So I've made a class and put the Grid in there. But how do I add it to the pages content without repeating lots of code and modifying the content already there? It needs to overlay what's on the page already... This is the Grid

Grid bottomGrid = new Grid { BackgroundColor = MainMenu.o_Options.BehindMenuButtonBackground, ColumnSpacing = 0, RowSpacing = 0 }; 
            bottomGrid.ColumnDefinitions.Add (new ColumnDefinition { Width = new GridLength (1, GridUnitType.Star) });
            bottomGrid.ColumnDefinitions.Add (new ColumnDefinition { Width = new GridLength (1, GridUnitType.Star) });
            bottomGrid.ColumnDefinitions.Add (new ColumnDefinition { Width = new GridLength (1, GridUnitType.Star) });
            bottomGrid.ColumnDefinitions.Add (new ColumnDefinition { Width = new GridLength (1, GridUnitType.Star) });
            bottomGrid.ColumnDefinitions.Add (new ColumnDefinition { Width = new GridLength (1, GridUnitType.Star) });
            bottomGrid.RowDefinitions.Add (new RowDefinition { Height = new GridLength (70, GridUnitType.Absolute) });