What characteristic defines proofing in K9 training?

Proofing in K9 training is specifically characterized by improving the dog's ability to stay focused on a task amidst various distractions. This process ensures that a working dog can perform its duties effectively, regardless of environmental factors that may typically divert its attention. By honing this focus, handlers can trust that their dogs will reliably perform commands in real-world situations, even when faced with challenges.

The other options relate to different aspects of dog training. Rewarding dogs for distractions would potentially take away from the focus needed during proofing. Practicing attacks on command pertains to protection or bite work training, which has a different objective than the focus required in proofing. Encouraging social behaviors in public also focuses on a different skill set, emphasizing a dog's interaction with people and other animals rather than their concentration on specific tasks. Thus, the emphasis on focus, inherent in proofing, is what distinctly sets this aspect of training apart.