Gunnar was a real tough sell on the speak command. I had to resort to teasing him into it.
Here's what I did:
I put him up on a 3 1/2 foot retaining wall in the back yard and had him sit, facing me while I stood down on the ground. (So he was elevated above me)
I had him on lead and put his ball down on the ground, next to me. I had him "stay" and blocked him from getting off the wall to get the ball.
I kept talking in a high pitched voice, really excited, and telling him to speak. As soon as he'd make a noise above a whine, I'd treat him and start over.
It took a while, but as he progressed to an actual bark, I'd treat him and then let him get the ball. We'd play for a while, then back to the wall and another speak/treat/ball session.
I eventually got him to speak on command and we eliminated the treats/ball.
I've done this with other dogs and had them speaking within about 20 minutes. Gunnar took several days to master what I wanted.
He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours faithful and true~ to the last beat of his heart. You owe it to him to be worthy of such devotion. ~unknown