when your saving process start then disable the button and when data saved than give message that your data has saved than after enable true this button i think after that your problem will solve
look this simple example
protected void Button1_Click(object sender, EventArgs e)
{
Button1.Enabled = false;
saveData();
Page.ClientScript.RegisterStartupScript(GetType(), "Script1", "alert('Data saved');", true);
Button1.Enabled = true;
}