Manage two CheckBoxes with one Boolean ASP

I want to set one boolean with two checkboxes : one is the opposite of the other. In my view ASPX, I would like to bind my second checkbox to the OPPOSITE 'isLocal' (comes from the database table, no model between):

<td align="left">
<asp:CheckBox ID="CheckIsLocal" runat="server" DataValueField ="isLocal" AutoPostBack="true"/>
</td>
<td align="left">
<asp:CheckBox ID="CheckIsPan" runat="server" DataValueField = "isLocal" AutoPostBack="true" />

In my code behind I trigger the check event for both and I try (failed) to trigger the other to change its value.

this.CheckIsLocal.CheckedChanged += new EventHandler(this.Oncheckedchanged);
this.CheckIsPan.CheckedChanged += new EventHandler(this.OncheckedPanchanged);

private void Oncheckedchanged(object sender, System.EventArgs e)
    {
        CheckBox CheckLocal = (CheckBox)sender;
        CheckLocal.Checked = CheckLocal.Checked ? true : false;
        this.CheckIsPan.CheckedChanged += new EventHandler(this.OncheckedPanchanged);
    }
    private void OncheckedPanchanged(object sender, System.EventArgs e)
    {
        CheckBox CheckPan = (CheckBox)sender;
        CheckPan.Checked = CheckPan.Checked ? true : false;
        this.CheckIsLocal.CheckedChanged += new EventHandler(this.Oncheckedchanged);
    }

I have two checkboxes for UI purpose, I thought of a ToggleButton but I don't know how to implement it without external tools.