Why did it chew the walls,,,Was it trying to get out???
there are two types of dogs inside and outside,,,no dog I ever knew got acustom to both... I inside dog usually keeps barking to com in and the outside dog trys to get out...

When a dog grows from a puppy neglected they need very special one on one training to be able to coexist with humans... the dog has to start to trust one person only before it can trust people,,,to many people is just to much to handle for him... I'm suprised the pound even gave the dog a shot...

if you can get it back you need to keep it outside and be the only contact for quite a while to have any chance with this dog...