How can I add guid querystring in my registration link

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MVC4

currenly my link goes as

"http://localhost:61435/NGOPortal/NGORegister";

but i want to add guid so this link is not use more then 1 time.. how can i add guid in my link ??

"http://localhost:61435/NGOPortal/a2cc5900-bdff-41f1-9c2a-21032a5275de";



and after registration same link can not be use for new regisration ..i am sending my code belove

What I have tried:

public void approve(ContactUsModel objModelMail)
        {
            var data = (from tbl_con in dbo_obj.tbl_contactus where tbl_con.Id == objModelMail.Id select tbl_con).FirstOrDefault();
            data.EmailId = objModelMail.EmailId;
            data.status = "Approve";
            dbo_obj.SaveChanges();
            string from = "ngoportal.jd@gmail.com"; //any valid GMail ID 
            string to = objModelMail.EmailId;
            using (MailMessage mail = new MailMessage(from, to))
            {
                mail.Subject = "Äpprove Request";
                string URL = "http://localhost:61435/NGOPortal/NGORegister";
                mail.Body = "Hi  " + objModelMail.Name + ", Please find the Registration Link. Click the following URL <a href="" + URL + "">http://localhost:61435/NGOPortal/NGORegister</a>  to Registration for NGO.Regards,ADMINNGO Portal";
                mail.IsBodyHtml = true;
                SmtpClient smtp = new SmtpClient();
                smtp.Host = "smtp.gmail.com";
                smtp.EnableSsl = true;
                NetworkCredential networkCredential = new NetworkCredential(from,"ngoportal123456");
              
                smtp.UseDefaultCredentials = true;
                smtp.Credentials = networkCredential;
                smtp.Port = 587;
                smtp.Send(mail);
            }

        }