Could douching immediately following intercourse act as contraception?

NO! . Douching does not work as birth control. Get accurate information and choose a birth control method that works for you. See: http://www.Plannedparenthood.Org or http://bedsider.Org/methods you may also want to learn about emergency birth control: http://ec.Princeton.Edu.
The right answer. Is to use protection for each and every act of vaginal intercourse. Douching after the fact will do nothing to prevent pregnancy.