sounds like a good tip that, sort of to let the dog know, you're in control and to let them off when its time to work, then back on the lead?
seeing a few of the replies its not surprising the rescue centres are chocked full. Binning a dog off because its got poor recall..? crazy.
I'm sure selling the dog to someone who has the time to teach an old dog new tricks is better than leaving the dog in the field altogether?