How do I get my dog to use the bathroom in the back yard ?

My dog has a huge backyard however he refuses to poop in it , only if I walk him does he then poop .When he was smaller I bought a pheromone stalk and that smell caused him to urinate in the back yard,he used to do it about a year ago but he stopped. Now he's 3 years old ....Can sombody share their experience ? please !

The best method that I have found for potty training a dog is the "Bells" method.Hang a string of bells around the door handle (use the door that you would take him out to go potty most often, so he doesn't get confused) and EVERY time you take him out, pause a moment to jingle the bells so he hears them. If you ring the bells and he goes potty *outside* he gets treats/praise/love. Pretty soon, he'll learn that jingle bells = potty time. Once he's fully trained, he'll jingle the bells on his own to let YOU know that he needs to go outside. One of the best things about this method is that the bells are transportable, should you need to leave him with someone else. Simply hang the bells at the new location and do a reminder round with him

My chihuahua does this randomly. I think she does it just for the hell of it or just being to lazy to walk to the door. I have to take her out every 20 mins for a day or so even if she doesn't have to poo and she catches on again. It's not happened many times but when it does this always works. It's like I have to show her how to do it all over again.