I have found that the best defense against random strangers walking up to you in public either to sell you stuff or to recruit you...is a good set of earphones. Bonus points especially if those earphones come equipped with noise cancellation because then, you have the legit excuse of not hearing them or your mother asking you to clean up the house.
But of course, for safety reasons, having noise cancellation as a permanent feature can be dangerous especially when you're out for a jog or cycling. This is why the new Sudio T2's option for you to turn it off and switch between active noise cancellation (ANC) and transparency mode is god sent!
But I am getting ahead of myself.