3 Answers

Timing with the feeding and putting him out is usually the best way to train the dog.  Also, frequent walks, rather than leaving him in too long will stimulate him to poop outside. 

What's his age? Have you been consistent in housebreaking him? Is he doing this regularly or are they accidents because he was not let out in a while. Have you had him checked for worms? Are you feeding him too much? Is there something that could be upsetting him? There are many reasons he could be doing this. You have to find the reason first, then see if it can be corrected. Jack Russells are very intelligent dogs. I'd be surprised if he was doing this just because he doesn't want to train. 

Hi take him outside just after you feed him. and praise him when he does his buisness.