I have a 4 year old Great Dane who is house trained. I would like to know if anyone has experience training a dog to always use a specific area, outside, to relieve himself, when not on leash.

It can certainly be done.
A lot of people train their dog to go in a certain place, usually a back corner.

The most common method is to purchase some cheap garden edging and make a 'box' on the lawn with an opening to walk through.
This will give the dog a better understanding of what you want them to do.

You then take your dog to this spot on leash to do their business.

It's the same principle as regular toilet training, if you see them go to poop on the lawn, you quickly take them over to the box.
If they go inside the box, praise them like crazy, make them think they have just done the best thing in the world.

I have a 4 year old Great Dane who is house trained. I would like to know if anyone has experience training a dog to always use a specific area, outside, to relieve himself, when not on leash.
I just saw a TV show about this yesterday -- a backyard makeover. The family's dogs were trained to relieve themselves behind a right-angled picket-fenced area in a back corner of the yard, so that the family could have BBQs without guests walking on soiled lawn. It took some patience, but consistency and lots of praise did the trick!