About two years ago I would have said "Pulling on the leash" because I just could not get Neka to stop pulling.
Now I would have to say: trying to remove "fear or aggression" from a dog after it has been abused by a previous owner. These kinds of dogs often shut down and will not allow anyone near them to help. I worked with one dog a year or so ago that was SO affraid of strangers that it would not even come to its owner if a stranger was standing there.
It took a long time to get him to trust strangers. But today, she is much better and when i stop to see her, she cant wait for me to come over and pet her!