I have several hopballs (aka tea balls) that i use to dry hop in the keg or secondary.
If i use it in secondary i can then rack into the keg and leave the dry hops behind.
If i dry hop in the keg then its stuck there till the keg runs dry!
I used to use stockings but bought 6 tea balls recently so use them. The only downfall with the tea balls is the little clip isnt stainless steel and starts to rust. Doesnt bother me, i figure i could always use a bit more iron in the diet......