Dinner starts. Your dog sits beside a chair, watching each forkful. Someone slips them a piece of food, and tomorrow they return to the same chair. They learned from a result, not from a rule they were supposed to understand.
Agree with everyone at the table: no food handed down during the meal. If the dog is already expecting scraps, give them a comfortable place away from the plates, perhaps behind a gate with their own food puzzle. This should be a pleasant spot, not a punishment for asking. Keep human food, especially potentially toxic foods, out of reach.
Make their own place worthwhile
When nobody is eating, put a mat a little away from the table. Reward your dog for stepping onto it, then for resting there briefly. Build a few seconds at a time and release them before they get up. Later, practice while one person sits at the table with an empty plate. Only then use a real snack, and keep the early session short.
During an actual meal, choose the setup your dog can manage. If a whole dinner on the mat is too much, use the gate and practice in smaller pieces at another time. Don't alternate between "never beg" on weekdays and handouts on weekends unless you're content with a dog who keeps asking. A food reward delivered on the mat, outside the meal, is different from a bite passed under the table.
If your dog has become suddenly ravenous, is losing weight, or is stealing and swallowing risky objects, ask your veterinarian about possible health causes. A predictable routine often makes meals easier for everyone, even if your dog still hopes for the occasional crumb. For more on building consistent household habits, see the everyday dog-training habits guide, meet health and feeding needs before changing the table routine
Sources: Petplan: How to stop your dog begging for food or stealing it. Best Friends Animal Society: Dog Counter Surfing - Prevention and Deterrents.