rad grid detailtables gridtableview column hide

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Telerik

I tired to hide a column of my Telerik Radgrid.I tired

rg.MasterTableView.DetailTables[0].Columns[6].Display = false;
rg.MasterTableView.Items[0].ChildItem.NestedTableViews[0].GetColumn("DeletePool").Visible = false;


tired on prerender event so ..but couldnot able to do so.
My Design is like that

My design is like this
 <telerik:RadGrid ID="rgPoolType"  Width="99%" AutoGenerateColumns="false" >
                               <MasterTableView AllowNaturalSort="true" DataKeyNames="ID" ">
                               <DetailTables>
                                        <telerik:GridTableView DataKeyNames="ID" runat="server">
                                            <Columns>
                                                <telerik:GridTemplateColumn HeaderText="Pool Name" SortExpression="Name" UniqueName="PoolName"></telerik:GridTemplateColumn></columns> </DetailTables>

Plz suggest ..