Our Bloodhound mix, at 4 months learned to scratch the door, to let us know, now at 1 1/2yrs old he still oes this, bu because it is a glass door, mostly he does this because he sees something he wants to chase. Now if he has to realy go out and potty he comes over and licks my arm! He has learned this all on his own, not sure how to go about and teach this.