Session 1. 10:00 am: Spend 10 mins with Sadie using a tennis ball that is attached to parachord. With Sadie in sit and down positions, durg the ball along the ground, and swung it in the air. When she made eye contact with me, marked it with "yes" and kept her in the command with "good girl". Released her with free to get the ball and let her keep it for a minute. Then gave command to "drop". When she dropped it, I marked it and and repeated the process.
Went to the park and played fetch, mixed with some rest and off-leash walking for about 45 mins. Played a little game when she rested in down position of rolling the tennis ball between her front legs. Gave command to drop, marked it, then rolled it back to her.
Session 2: 7:30 pm: Repeat of the park above.
Sadie is reluctant to drop the tennis ball when off leash in the park, unless she sees the other tennis ball in my hand. She knows when I am holding the other tennis ball, she is probably going to get to run after it, so she drops the one she has in her mouth.
Reduce Sadie's need to keep the tennis ball when playing fetch. I will let her see that I have the other ball in my hand, but I will place it behind my back so it disappears just before she drops the one she has to get her conditioned to drop the ball when the other ball is out of sight.