I used a neck cord with mine. Just to be on the safe side, I went ahead and tied a hitch into the string as I approached the track, but the person sitting next to me did not do the same with the cord on his sunglasses...but yes, he had a neck cord.
I noticed that several of the operators are bespectacled; given the amount of difficulty we did not have, I am guessing that these operators have ridden, and determined from experience that the loose neck cord is probably sufficient.
Bottom line is, secure your glasses with something. They seem to be fairly tolerant of whatever something you happen to choose.
(By the way, LLTID, you will be interested to hear the the Iron Dragon trains were all repainted. The drab green is now a gorgeous metallic finish, and the drip pans are a gloss black. The track is still faded red, but the trains are spectacular.)
--Dave Althoff, Jr.