How do i stop my dog pooping on the patio?

I have two female dogs, one a 10 year old lhaso apso called Polo and a 5 and a half month old german shepherd called Sasha. The problem that i am having is sasha keeps doing her business on the patio.I don't know whether or not it is to do with Polo but i feel that its something that i should iron out now whilst Sasha is still a pup, anyway Sasha also goes on the lawn and patio but all i want is for her to do it on the lawn.Oh ive done abit of research and people are saying put the dog on the leash and make it go where you want it in this case the lawn but the problem here is that Sasha lives outside.