Housetraining a shelter dog

Question
We have a 2 year old Terrier mix that we adopted a few weeks ago at our local shelter. We are crate training him..he does really well with urinating outside, but, pooping is the problem. He is fed twice a day, and after he eats he walks right up to the door..we take him out, but, he doesn't poop! He goes back into the house, and if we are not watching him closely, he goes into the garage and poops. Our 7 year old cock-a-poo goes outside and does both with no problem. We have walked him all over the yard, have left stools on the lawn for him to smell. He finally went last night after not going for 2 days! He is neutered. He is in the crate from 7:00 a.m. until 12:00 noon, then from 1:30 p.m. until 5:00pm. We take him outside when we let him out of his crate, and after meals, and at 1 hour intervals after that....just do not know what to do with this dog.Suggestions are very welcome.

Answer
Much of what you are doing is right.  Keep walking him.  They can only walk and hold it so long.  A game of fetch might be less tedious.  Just keep him moving.  Once he finally has a bowel movement, lavish praise on him.  

If you must give up and bring him inside, either keep an eye on him or crate him.  Keep the door to the garage closed.  If you see him go to it, take him out.  Out up gates, tie him to you or the computer, whatever to keep him in view.