jools - There is no such thing as a 'sure cert', they don't exist.
All you can do is shorten the odds are far as possible based on factors you can plan in advance.
But there is always an element of chance involved - always.
If you have the nerve to risk it, and your plan comes off, then fine, but think about this - if it was as easy as you want to think, why are not thousands of people doing it every day?
If something sounds too good to be true ....