Keep poking and weaving material in, I don't use to string to hold anything in place, but I do find a bradawl or small screwdriver is helpful for making places to poke new material in.
From the guardian.co.uk
However I did explain in New York that I didn't want my sashimi flapping about thankyou, whereupon the chef promptly despatched the little bugger with a bradawl before slicing it in front of me.