Hi Abstract,
I have a few suggestions.
First, although it will sound gross, take a piece of your pup's feces and put it outside where you want him to potty. When you take him outside, lead him to it and have him sniff it. Dogs often stimulate themselves to defecate by smelling old poop.
Second, be careful about disciplining your pup when he has accidents in the house. If you don't catch him in the act, you really should just quietly clean it up while vowing to watch him more closely!
. Yelling at him or punishing him in any way leads to a dog who is afraid to "go" in front of you.
By the same token, if he acts at all interested in pooping outside (circling and sniffing, etc), don't stare at him. Turn sideways, fake a yawn, act uninterested. Then, when he's finished, it's party time: lots of excited praise and yummy treats (which you will have with you so that you can reward immediately).
Hang in there! He'll get it.