I am training a small dog for competition obedience. He does nicely on leash, but as soon as the leash comes off, he loses focus. What should I do?

Question from Cindy: Hi, I'm training a small dog in competition obedience and I'm having trouble transitioning to off leash exercises. As soon as the leash comes off, her focus starts to waiver and her heeling becomes less precise, sniffing and lagging when we start. Having a leash tab or string drag line doesn't work well for me because of the time it takes to bend over and reach it. I'm going back to marking and rewarding for brief moments of focus, like every few steps. Is there any other advice for a dog becoming leash wise and/or ring wise for that matter?