A dog's defensive drive is the drive to protect itself from a threat. When an untrained dog is working in its defensive drive it thinks that it's in a position where it is being threatened or attacked and as a result it is stressed. For progressive defense training we want a dog, that even though it is unsure of its position, it will initially react to a limited amount of threat with an aggressive challenge. Willingness to defend himself is inherited from his parents. It cannot be trained into the dog no matter how hard you try. If a dog has not inherited the defensive gene there is no way we are going to make this dog a protection dog. A few good examples of this are most labs, golden retrievers, huskies or other such breeds. 

First build up your dogs prey drive with motivational toys like a jute tug, play tug o war carefully making sure you let your dog win enough to keep his drive high. When he wins it praise him and let him have it for a minuet or 2, DON'T hassle him , but when you say 'out' or what ever your command is to give up the toy, make sure he lets you take it. once in your possession repeat. Soft rubber balls are good motivators too, throw them, bounce them close, hide the ball in long grass let him locate it and praise him when he finds it. 
you can teach your dog everything in prey drive, you can even get a bite sleeve and train bite work, but you will only know how far your dog can go, with the help of a highly skilled agitator/decoy that knows how far he can push a dog before it goes into avoidance and runs away.. 

The only time your dog should start defense drive is after he has reached mental maturity sometimes 2-3 years old and only after he has gone through the foundation work in prey drive. 
Working defensive drive takes a highly skilled helper that is experienced at reading and understanding temperament and knowing exactly how far a dog can be pressured or threatened in defense before it is pushed into avoidance.