Do you just leave one pad out? My baby is good with hers but I know a lot of yorkies are picky and don't like peeing and pooping in the same spot! If you have just one pad out, maybe try putting out another one to see if he might go there. If you see signs of him about to poop (sniffing and walking in circles, or even just about to squat) and take him to the pad immediately. Keep him there until he has no other choice but to poop on it! And when he does, praise and praise and praise and treat
It might take awhile but he should eventually get it!
As for the walls, have you tried any sort of spray on it? I used bitter apple when Layla was going through her chewing stage, but it didn't phase her at all. What worked for me was clear deodorant. She also chewed on the walls, and on the wooden handles of my desk, and the wooden coffee table legs, and basically anything she could put her teeth on. But she got a taste of the deodorant once and wouldn't go near anything that smelled like it anymore! Since it's clear it doesn't really show up on walls or furniture. If you have just a few problem areas I'd suggest trying that!
Good luck!