My 9 year old dachshund has no problem with "going" outside, but he's very particular about where he poops. We've just moved into a new house with a fenced yard and soon will be able to just let him out when he wants. Unfortunately, we haven't got a huge yard and I'd like him to use the bathroom in a location that won't be heavily trafficked, which, unfortunately is exactly his favorite spot. I've had no problems with getting him to pee in the right spot, but he just refuses to poop in the corner of our yard where I want. The spot does have grass.
A combination of things that could work (there is never a guarantee) are:
Move the feces into the toilet area. The smell of urine and feces is usually what signals the toilet area to a dog. So tell him where you'd want him to poop by moving his feces out of the highly frequented area and into the designated toilet area. Don't pile them up there, keep a few old feces lying around and remove the rest of them.
Offer an alternative resting place. Why did your dog chose to poop in the highly frequented area? Maybe because he likes lying in the less frequented area because he won't get disturbed there? Or maybe because there's a tree or bush and he likes the shade? Or maybe there's no tree or bush and he likes the sunlight? Try to offer him an alternative to make it easier for him to adapt to the new usage. That could be an outdoor dog bed somewhere or an area where he shouldn't be bothered by anyone passing by.
Be prepared to admit defeat. If your yard is too small to offer your dog an alternative favorite place, you won't have much luck. If your dog has a strong and independent personality, he will out-stubborn you. If you don't keep your yard clean enough of feces, he will start pooping all over the place.
I have a Golden Doodle, and getting him to poop and pee in one area has been a challenge. It takes time and patience, but the best way is to leash him, and take him to where you want him to poop until he does. You might be out there for a while, as dogs don't like to poop in unfamiliar spots. If they do poop elsewhere, gently reproach them, and lead them to the area you want them to use. When they poop in the desired area, praise them liberally, and treat and pet them.
Hope this helps. :)