I have two collies, both rescued at 6 months(ish) dog2 has always been very nervous, he used to wee everywhere and duck his head to the ground if anyone/thing walked/ran by. He has started barking and pulling if we see another dog when we're out and he's on the lead, he is pretty big and probably looks quite intimidating, if I see the other dog first and can get him to sit and stay with a treat then he is ok but otherwise he barks and pulls until they've gone. He is fine when off the lead and will run around and play with any other dog. I'm not sure what to do now...