question about button of "logout"

hi
   i'd like to ask a question.
  my webform,in Page_Load,i have a code to check whether the sessions are right. and the for the button of logout, i first do  System.Web.Security.FormsAuthentication.SignOut and abandon all sessions,then  Response.Redirect login page
   and i hope that when the user click button of logout,i hope that the code of Page_Load is not executed but directly execute the code of button of logout?(it seems i cannot set a button's postback as "false"),neither cannot i use "postbackupurl" coz it will not execute the code of  System.Web.Security.FormsAuthentication.SignOut and abandon all sessions in button click event
  thank u very much
best regards