We have 2 big boys (dogs) that were our first babies too. We eventually dug up a planter area when we moved into our last house and put pea gravel in it for a dog area after the dog urine was burning our entire small grass yard. We taught our boys to "Potty in the rocks" with a lot of persistance and patience and of course treats. You will want to lead them out to that area (likely on lead)when you know they need to go to the bathroom. We label everything with the boys so we would say as we were doing it "Go potty in the rocks". They also had a "Go potty" and "Go dukie" (poop) command, so that helped but it definately is not necessary. Give treats like crazy at first when he/she does it. You can work your way up to having them go out on their own, but make sure they always go in that spot otherwise the habit is too easily broken.
Good luck. It is a lot easier having one designated dog spot. Oh, we also tried one of those plastic things you can buy that are suppose to be scented to help them go in a certain area, it didn't work. The best thing was having them use their own scent and being really really consistent and give lots of treat. We now can tell them before they go out the back door and if we see they are heading to the grass can say, "no grass, potty in the rocks" and they readjust thier direction and go in the correct place.