My older GSD was not a natural retriever, but we worked out a "fetch" method that she loves without needing any compulsion/force fetching.
Figure out your dog's most valuable, prized toy. The thing that s/he loves above all else. For mine, it's currently a squishy ball on a rope (used to be a floppy Frisbee). Don't throw the Most Valuable Toy, keep it in one hand. Throw a different, lower value, item with the other hand.
When your dog chases and picks up the lower value toy, praise. Swing/toss the Most Valuable Toy around in your hand, and then when your dog brings the lower value toy back to you, praise some more. When your dog brings the lower value toy to your feet, praise a bunch and quickly offer the Most Valuable Toy for some tugging and happy noises.
It might take some repetition, and some patience, but I'd recommend putting away the Most Valuable Toy and only bringing it out when you are practicing this exercise. It taught my non-retrieving dog to looooooove fetch, and she'll retrieve anything now. Sticks, balls, shoes, whatever you tell her to.
This method also helped teach both of my dogs an enthusiastic water retrieve. They aren't allowed to shake/shred/tug their floating bumpers. When they do a really nice water retrieve and drop the bumper at my feet, they're rewarded with an appropriate tug toy.