We run a contain drill to close every practice. we start with three defenders and one rabbit. The rabbit lines up head up with the middle of the three defenders. Rabbit runs side to side (10-20 yds), the middle defender mirrors the rabbit and theother two keep the rabbit to his inside shoulder. We reduce to two defenders on one, then one on one. The second drill for your DE is how not to be hooked and how to string the runner to the sideline--down the LOS. You might consider adjusting coverage to enable your DE to bring pressure and a LB picking up the coverage man to man. Drill you DE to rush and attack the outside shoulder of the RB (rabbit drill) and to cut him off if the flares. The DE cannot let the TE or RB to cross his face to get to the outside. Your problem is the same in all defenses, contain. I coach 8-11 year olds Junior Pee Wee division. We run multiple defenses-52, 53, 4-3 and 60. We emphasize contain responsibility and stringing out the play to the sideline. Get them to cut off the runner by going down the LOS instead of attacking them in the backfield. Good luck.