Winston loves to control other dogs with his paws. If dogs annoy him, or if he doesn't want to play with them, he swipes them over the head with his paws. Some other common things that dogs use to communicate 'stop' or 'no' are: muzzle punching, lunching, snapping, growling, barking etc. Winston utilizes several of those strategies, but he really loves swinging his big Mastiff paws when he wants a dog to leave him alone.
As you can see in the video, it is very effective.
*This video exists in order to educate people about dog behavior at dog parks.*