There are a few preventative measures you can do with your dog to lessen the likelihood of problems later on. Unfortunately, even if you have the best intentions and do all the exercises properly, there are no guarantees of eliminating the problem later on. Regular maintenance is also a good idea.
Barrier Frustration can occur if a dog is behind a window, fence, or on leash and is not allowed to interact with the environment. After a while, she may get frustrated and aggressive. One indicator of Barrier Frustration having a part in aggression is if a dog barks behind barriers and is calm around dogs when off-leash, but is very aggressive behind a barrier or on-leash. Dogs, of course, can also show aggression no matter how much they are being contained as well.