Hola Espero que esto te sirva, Saludos...
<head runat="server">
<title>Untitled Page</title>
<script type="text/javascript">
function clearTextBox()
{
var txt = document.getElementById("TextBox1").value;
document.getElementById("TextBox1").value = (txt == "00-00-000-0000")?"":txt;
}
function setTextBox()
{
var txt = document.getElementById("TextBox1").value;
document.getElementById("TextBox1").value = (txt == "")?"00-00-000-0000":txt;
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:TextBox ID="TextBox1" runat="server" MaxLength="14" Text="00-00-000-0000" onfocus="javascript
:clearTextBox();" onBlur="javascript
:setTextBox();"></asp:TextBox>
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="TextBox1"
ErrorMessage="Error debe de ser el formato 00-00-000-0000" ValidationExpression="[0-9]{2}[-][0-9]{2}[-][0-9]{3}[-][0-9]{4}"></asp:RegularExpressionValidator></div>
</form>