I have a puppy that poos outside in the garden. However, she is not selective in the location where she poos, and the garden is relatively large. This makes the weekly clean up a bit of a scavenger hunt, and it's easy to miss one or two, which makes walking on the garden a little less pleasant. It would be easier for us if she went to the toilet in a more limited region of the garden.
What is a good strategy for training a dog to poo in a particular part of the garden?
Ultimately positive praise, reward, and repetition are the keys.
When taking him out after meals, try to direct your dog to the particular area in which you would like him to relieve himself. You will have to stay with him and try to encourage him to remain in that area until he goes. Once he does, provide him with positive praise and rewarding him (food rewards obviously will work best). And keep repeating until he picks up on the idea.
However, just like with paper training an apartment dog or regular house-breaking, accidents will happen. It is important that you do not punish him for going where you don't want him to go, especially very early in the training. It will only confuse him and possibly associate the punishment with going to the bathroom, which will complicate matter significantly.
After meals, I take my dog to a particular place, somewhere near a field in my house. I say to him in my mother tongue for him to poo. As you all know, pets follow reflex actions, after somedays practice he will understand what you want him to do. But sometimes, I also observe rather than you picking an appropriate place for him, he will choose one himself, which is most likely you would find appropriate too. In day 1 , if he poos somewhere you think okay, take him to that place on day 2 too and say him to poo and try not to let him someplace else go. If he poos, 99% sure he will mark that place and from day 3 he will take you himself there. Also, praise and appreciate your dog when he poos. Give him rewards, that way, he would better understand you. Best of luck :-)
