kaiser wilhelm

I have a problem with an 18 Month old Malinois, he is capable of biting deep and firm.However when doing sleeve work he will be hesitant coming in and wont bite full and deep, and will also relax his bite giving the sleeve up very easily. I was thinking of using a bungee line to help overcome the problem, but havent used one before.What length/strength of bungee is best, should it have a quick release clasp? Should I go back to starting with a bite bar, then soft sleeve, then schutzhund sleeve, as the bite improves? Can anyone give me some advice on exactly what is the best method of using the bungee line? A step by step explanation would be of great help. Or if anyone has a video feed link that shows it being used.