if he is still coming to you when you ask him to sit, run towards him and make him sit where you ask him to, by moving towards him giving your sit command, he will/should sit, you have to act when your dog doesnt listen and not when its at your feet as by then its too late, hope that makes sense, im no expert but it has worked for me and i have been told similar by those who are experts
i understand thanks i will start to introduce see how it goes.