2001年，杜大卫重返中国，到北京第二外国语大学任教。从那一天—2001年8月28日起，他自愿担任纠正北京的旅游景点、街道、博物馆等公共场所的错误英文，他的尽心尽力引起了社会各界高度关注，被北京人喻为“英文警察”，也为建设2008年奥林匹克运动会语言环境做出了突出贡献。今天，已经在北京声名远扬的杜大卫还会自觉地去纠正他生活中看到的错误英语，“纠正错误英文”似乎已经成了老杜生活的一种习惯。
In 2001, David Tool returned China and started his work at the Beijing International Studies University. From that day, which was on August 28, 2001, he voluntarily undertook the work of correcting the errors in English signs in public areas of Beijing, such as scenic spots, streets and museums. His earnest attitude and efforts attracted attention from all walks of life and he was honored as the “police of English.” He also made outstanding contributions to the improvement of the language environment for the 2008 Olympic Games. Today, David Tool, who has become a household name in Beijing, still consciously corrects the English mistakes that he sees. It seems that “correcting English Errors” has become one of his living habits.