How are you doing the training? Some ideas... don't stand still, keep good constant motion, use perky voices, leash the dog so it can't get away from you, keep the sessions short (once he starts fading that should stop the session and likely less than 5 min). Food lure (let his nose touch the treat), keep it fun. Pure motivation. If he's hot, tired, too distracted, don't train. if he does better on the deck, for every 3 commands on the deck run to the grass to do one, while maintaining his focus and quickly run back to the deck (make him chase you). Train for engagement on the lawn first before commands. Find his motivator and use that on the lawn. Withhold his meals and use meals as the reward for those training sessions (feed by hand). You'll get there!