navigation - How do I stop people using the back browser button after they have left my site so they cannot return? -

i need safety feature - subject of site sensitive (domestic violence) - have safety area on site , if clicked person taken out of site 'safe' site.

once have clicked area stop them coming nominated period of time - (say 1 hour) - if abuser came room escape site, , if hit button not obvious site looking at.

ideas??

you capture button event , send user random "safe" url using like;

window.onbeforeunload = function () {    location.replace('http://www.bbc.co.uk');    return "this session expired , history altered."; } 

within function block set cookie called 'noreturn' whenever pages on site check redirect each time "safe" site next hour.

there's decent article on aspects of controlling button , user's browser history here;