how to make a Mutually Exclusive CheckBox, Compulsory

Hi all

Is it possible to make a Mutually Exclusive CheckBox, Compulsory?  If so what do I need to use as I can't see how the  required Field Validator would work on the below?  

<asp:CheckBox ID="chkBoxBPYes" runat="server" Text="Yes" /><cc1:MutuallyExclusiveCheckBoxExtender ID="cboBPYesExtender" runat="server" 
      Enabled="True" Key="benefitProtectionChoice" TargetControlID="chkBoxBPYes"></cc1:MutuallyExclusiveCheckBoxExtender><asp:CheckBox ID="chkBoxBPNo" runat="server" Text="No" /><cc1:MutuallyExclusiveCheckBoxExtender ID="cboBPNoExtender" runat="server" 
      Enabled="True" Key="benefitProtectionChoice" TargetControlID="chkBoxBPNo"></cc1:MutuallyExclusiveCheckBoxExtender>