The good news is that it doesn't seem to be a health issue. Not everyone goes twice a day, or even once a day. There is great variability based on a number of issues. Our dogs are fairly predictable and twice a day is about right -- with exceptions -- but other dogs could be different. If you're concerned, I'd think diet would be a big factor. If you are aiming for twice a day then elbrant's suggestion of pumpkin (the whole not the pie filling) might help.
Sometimes your idea of how diet works can be off. This week one of our dogs managed to grab a bag of minnow treats and eat most of the bag. We were expecting a runny explosion but her scat was unusually hard. Go figure.
Along the same vein, not wanting to defecate in the backyard is usual except when it isn't. A lot just depends on the size of the yard, number of dogs, and so forth. And perhaps how they were raised as well.
We've had dogs who weren't happy in the dark outside. Some were unfazed. Your pup seems normal.