My doberman puppies 7 and 8 months old have started pawing the back of my legs as we go outside or walk down the hall. They do it frequently and do it pretty hard. Any ideas as to why they are doing it? It will almost knock me down at times because they seem to be aiming for behind the knees. I had a sitter stay with them for the holidays while I traveled and they did it to her also. She didnt expect it and it made her fall. I am now trying to break the habit by saying no and stopping each time. Would like to know why they are doing it so I would have a better take on how to break them.