Zeeva, we started with small distances under control with a leash and worked up the distance. We started with our 6 foot leash to teach the command. Once she was solid with the 6 foot leash I moved to the 20 foot cotton lead, just to be sure I had ultimate control in case she tried to bolt off after a squirrel. The lead was simply for control; we simulated stay and recall as if there was no leash involved.
Off leash, we started over in our closed garage, using only 6 feet or so of distance. Once that felt solid we moved outside into the yard with no distractions, and gradually increased the distance.
The secret, imho, is to move in baby steps. Many, many reps are needed to clearly teach the dog what you expect, and every new change you introduce (distance, new lead, new location) means that the dog is likely to "forget", so you have to be patient.
The final step was on the 20 foot lead with distractions, ie, other people walking their dogs on the side of the street just a few feet away. Liesl broke her stay many times during this phase, and when she did I just shorted the distance between me and her and lengthened the distance between her and the distraction to find that equilibrium that allowed me to keep her attention. Once it was solid, we reversed course and I got farther away while letting the distractions get closer.
We now walk off leash, 10 feet from other dogs, and she obeys my "leave it" without fail (unless the dog is a friend of hers, in which case it turns into a tail-wagging and face-licking party. We're working on that.)
Liesl, b. 1/1/11