I teach grass barriers, I start with a long lead or a flexi and play loads of chase games(AKA dog chases ME, never ever ever the other war round) when the dog gets near the edge of the grass I ran away bouncing and calling lik "oh happy day!" lol when the dog comes running(placing front paws ON me) I praise and praise like no tomorow, play tug and such. once the dog has that down at least 99% of the time I start letting the dog off leash for short periods, when apporching the edge of the grass, run away calling and bouncing, when the dog comes a running more praise and games. eventually they figer out that edge of grass mean run back to mom! I have never had issues with this, and I have done this with 3 dogs and it has yet to fail. it was pretty funny how impressed people were when a biker went by on the other side of the street and Misty went galloping and barking right to the edge of the grass and went right into a U-turn back to me as soon as she reached the edge lol