Trouble getting dog to use bathroom outside

So I recently moved into an apartment and one of my dogs, an Australian Shepard not even 2 years old is having trouble using the restroom outside when I take him outside. At our previous location, my mom's house he would go freely outside in the backyard. He will literally hold it at the apartment almost the whole day before finally unleashing it all on on the training pads. Obviously glad he's at least using the pads, but I feel terrible that he holds it 12+ hours because he seems scared to do it when I walk him outside. I've tried the petsmart spray that is supposed to alert them where they can go. Any help would be appreciated, thanks!