He really ought to go back and talk to folks my age. Here is what I would tell him.
"Ryan there is a seldom used, but very effective, method used in football. Or at least it used to be used, and it works well. It's called a huddle. Let me tell you how it works. I'll explain it slowly, so you have time to take notes. After every play, you have your players meet together in a group (hence the name, huddle) about 7 yards behind the line of scrimmage. Then, you have a player standing next to you on the sideline. You tell him the play you want to run. He runs onto the field as a substitute. Another player runs off. Make sure you do this. Even with a huddle, 12 men on the field is still illegal. This player tells the quarterback the play. The quarterback then tells the group (the huddle) the play. He yells "Break!" and the players leave the huddle and line up for the play. See, it's almost impossible to steal signals with this method since there are no signals. You might want to try it. While Venables is trying to steal signals and his players are looking to him to tell them what the play is, you might catch them off guard. I know it sounds ridiculous, and you are probably to young to know anything about a huddle, trust me. Go back and watch some films of games played 60 years ago and you'll see it."
He would probably ask me, "What is this "film thing" you are talking about? And, anyway, this seems way too complicated."