If you are wanting a defensive bark, find someone to come to your house at night and be out in the yard with your dog. Have the person who is outside of your fence make some weird sounds or tap your fence with a stick or anything that might cause your dog to be suspicious and give him your command to bark. If he lights up, praise him up a lot and have the person run off. One thing I noticed is that your verbal praise it too subdued. It should be very animated and exciting, along with more enthusiastic petting up of the dog.Then after a few minutes, repeat. Do this about 3-4 times and end on a high note. If it works, continue to do this approach a few times a week and then you can transfer it to a person acting strangely who is in site of your dog if that is your goal.