If (and this a BIG 'IF') one decides to use a Walkman then surely it is de rigueur to wear the fashion of the era? Headband, spandex and hi-viz pink leg warmers... just to alert you to any cyclists, of course.
And, if a runner decides to wear an I-pod (Aye-pod in Tartanshire...) then why not allow marshals to eyeball and, where appropriate, life a placard that informs 'Concealed marksman ahead dislikes runners with headphones' or 'You won't hear that bus before it hits you!'? Perhaps confrontational and little OTT?
Still, I really benefited from the joker who held an audio device in his hand at Brid half and played - without earphones - motivational blurb to get him round... certainly made me want to get ahead of him!
NtS