dog toilet behaviour

Question
We took in an abandoned dog 2 years ago.  We believe she is about 7 years old.  We live in the countryside in a property with a lot of land including pool, garden, allotment areas etc.  Pip, our dog sleeps outdoors.
In 2 years we haven't been able to  train her to poo in appropriate places away from the house, pool area, garden etc.  She is free to roam on our land and on neighbouring lanes and tracks.  
The problem seems to be getting worse, for instance today she was reprimanded for pooing on the lawn.  Our current response is to take her to the poo and smack her nose and say no. This seems to have no effect whatsoever.  We have young children and my partner and I are becoming increasingly distressed by this situation.  Your thoughts and advice on this situation would be greatly appreciated.  Many thanks for your time and cooperation.


Answer
Hitting a dog for ANY REASON is totally OUT of the question.

Your dog is a very mature adult beginning to go into old age.  She does not understand that there are "appropriate" areas for her to eliminate. It's also extremely inhumane for this dog to be forced to live outdoors.      If you want to train any dog to eliminate in a specific area, you observe the elimination schedule of the dog, keep it on leash, take it to the appropriate area, and use POSITIVE REINFORCEMENT to reward its elimination.  Do this repeatedly for several weeks and hopefully your dog will form a conditioned response and begin to use this area, but random persistent reward must be given for some time (months) in order for the dog not to begin to generalize and wander from her designated area.  This does NOT mean the dog is tied up or restricted, it means YOU have to go with the dog and reward her appropriate choice of area when she needs to defecate.  Furthermore, you might worry more about the lesson your young children are learning by observing you physically punishing an animal and forcing her to live outdoors.  Poop can be (and should be) picked up on a daily basis; cruelty begets cruelty.