RadRating on click

Hi, 

how do i put RadRating in the ReadOnly mode when clicked once. the same person should not click on the radrating twice. thank you. 

<telerik:RadRating ID="ratingBar" runat="server" AutoPostBack="True"
            ItemCount="6" OnRate="RadRating1_Rate" Orientation="Horizontal" Precision="Item"
            Skin="Outlook" Width="100px"></telerik:RadRating>