When my 4yo is sent to his room, I cannot get him to STAY there. He knows how to get the doorknob cover off, and I can't lock the door from the outside. He may also lay there and kick the door until I want to go up there and break both his legs!!! I have a 6yo, his 4yo twin sister, and a 2yo. I don't have all day to keep putting him back in the room. Help?