You need to use JavaScript to alter the link once it's clicked to prevent future click handling, before allowing the page to proceed with the postback. A naive attempt would be,
<asp:LinkButton runat="server" id="button" OnClientClick="this.href='#'">
Click - doesn't quite work
</asp>
This successfully prevents successive clicks from triggering the postback, but it also prevents the first click from triggering the postback. A little more logic is required to make this work correctly. In the codebehind, I grab the actual postback JavaScript snippet and work it into some logic.
protected void Page_PreRender(object sender, EventArgs e)
{
button1.OnClientClick = string.Format(
"if(this.getAttribute('disabled')) return false; {0}; this.setAttribute('disabled','disabled'); return false;",
Page.ClientScript.GetPostBackEventReference(button1, null));
}
In the HTML template:
<asp:LinkButton runat="server" id="button" >
Click - does not allow multiple postbacks
</asp>
You can spruce this up with some CSS, and at that point I would advise including jQuery, so your code is more concise (due to its command chaining).