If every guy reacted the same way to "no" then it would be easy, at least the same approach could be used by all women. Unfortunately they don't. Some take "no" as an invitation to try harder. Some take it as an insult. Some take the hint. How those responses manifest are as varied as the individual - "no as an invitation" could result in some serious stalking activity, "no as an insult" could result in assault or worse.
The trick is in trying to read the situation and the individual. How is he going to respond to "no", what will he do? Part of that is the way in which the "no" is delivered, if it is rude and aggressive it might escalate the situation or it might be the circuit breaker you need. Not forceful enough or too polite and you might not be taken seriously. So hard to know. So damn hard to know!
Just had a close brush with it myself, fortunately my request that he go away was taken up but even that was freaky. That I even had to point out to him that his behaviour was inappropriate was troublesome.
