Look around for 550 paracord, in appropriate colours I bought 100ft of dayglo orange, with a reflective thread through it for my tent last year, to replace the red paracord it came with. Ideal, nice and bright in daylight, and you can see the tent 100m away in the dark, with a good torch. Not sure if I bookmarked it, I’ll have a shufti.
[edit] I got mine from eBay! but dx.com do it here:
http://dx.com/p/reflective-multi-purpose-paracord-nylon-rope-cord-orange-red-105664
Note: fluorescent is no good in the dark, you need the reflective thread as well, fluorescent makes it easier for clumsy muppets to avoid tripping over the lines in broad daylight.