Avoid users to double click on Submit Button in ASP.Net

Hi,

I added below Code to avoid Double Click by the Users on Submit button.

But sometimes still we are getting Duplicate Entry in Database Table with in a Fraction of Seconds gap.

<asp:Button ID="btn5" Text="Submit" runat="server" OnClick="btn5_Click" UseSubmitBehavior="false" 
    OnClientClick="if(!confirm('Are you Sure, Do you want to Submit?')){return false;}if(!Page_ClientValidate()){return false;}this.disabled='true';this.value='Please wait....';" CausesValidation="true" CssClass="submit" />

How to Handle this, Any body can help me.