I make my own nets and for a four foot net put 12 foot of drawcord on them , thats plenty enough to wrap round them and hold them , like you i wouldn't use elastic bands and carry them on my wrist some jobs my hand to my elbow would be solid with elastic band . if you count them out and count the nets in you shouldn't loose any but i often count then at lunchtime and close of play so if a nets missing you know where to look for it
With colored spun nylon its certainly harder to loose a net but i favour brighter drawcord as if your not concentrating a rabbit back netting itself all youve