I use a 20' piece of rope square-knotted to a dog leash clasp on one end and a D-ring on the other.
The D-ring can be used to attach it to another 4' or 6' leash which, in Laurel's case, was looped around my belt at first for "hands-free", then later we moved along to just a "drag line" in case of emergencies, and finally we achieved reliable enough voice control to take her off leash on the trail.
I did not think the retractable was safe enough or me or a 6 lb puppy so I never tried one. I use a 4' lead in the city and a 6' for training and on-leash hiking with Laurel.
Laurel: born 9/1/18, 7 lbs, my homegrown
Chocolate: born 10/4/18, 9.5 lbs, rescued from DV situation