Biffy is with a dog walker now twice a week just to give him a little more stimulation during the day etc... He is obviously a hard wired farm dog , he is currently on the lead for most of the walk with the dog walker untill sh feels comfortable with biff off the lead and she is only doing the off the lead in small sections of the walk. She is also very good a will select the dogs to walk with each other as a match. however yesterday she mentioned to me that when he is playing and running with the other dogs he will try and nip the back of the legs of some of the dogs when chasing and actually trying and herd them in the way he knows..... but she said its only with black dogs??? different breeds but really pays attention to black dogs and wont do it at all to the others?? I honestly have no idea on this one and cant seem to find anything on the web for it.... any ideas?