Is he assuming your command to send him? He may be picking up on your body movement that you do right before you make the send. Like for me, I didn't realize I was saying "Annnnndddd BACK!" and I'd get so pissed for him "breaking" on me until I watched a video I recorded and realized I was actually sending him before I wanted him to without realizing it. You just might be making a body movement to making a certain sound they've picked up on, or it could simply be timing. Like are you trying to send 2-3 seconds after the mark every time? Break it up. Send some immediately when it hits the ground/water, some send him 8-10 seconds later. Even some, walk away from him for a second and come back to him and send him (which this is later on). Don't give your dog hints to go. Be quiet and still as possible and change your timing.
