I’m afraid my opinion is that the dog’s lifestyle is largely to blame. Containing any dog in a kitchen day and night all through the week will make him bored, even if you do spend time with him in the evenings. The chewing is a simple reaction to his boredom. Don’t think that he is intentionally trying to ‘get back at you’, he simply found something to do which would occupy him for most of the day. When you are at home at the weekend, take him on a day out where he will be outside all day. When he relieves himself reward and praise him immensely. Repeat this as often as you can. If he thinks he’s meant to do the toilet in your kitchen then he will try to for as long as he is near to it. Try and get him used to ‘pooping’ outside away from your home, and used to being rewarded for it. He may then learn that even when he’s in his own garden, its good to do his business outside, and not in the kitchen! Also, when you spot him squatting in the kitchen ready to go, immediately move him outside, and even if he does not actually go once you have moved him outside, still reward and praise him while he is there.

In the long term, I hope you will consider having a friend coming to your home at lunchtimes to take him for a walk, or trying to find day-boarding for him while you are at work.