inserting a date into a cell

Hi people,

I have a spreadsheet that has a button that inserts todays date into a specific cell using the ()TODAY code. No problems here.

When i re-open the spreadsheet some other date in the future the date will obviously update itself to the current date. How can i stop this from happening? I only want the date that is entered when the button is pushed to stay there forever, no matter how many times on future dates its opened.

Any help would be greatfully received

Thanks