Interesting. I didn't have a problem with the uneven background as much as with the shadow. I shot with a flash, and bounced it with a better bounce card arrangement. What are your suggestions for eliminating that shadow, absent studio lighting and using flash only? Is it even possible? I tried to shoot without the flash, and bump up the ISO, but I couldn't get enough shutter speed, and the pups were moving too fast.

As you can tell, I'm in deep learning mode......