Pooping in his kennel

Question
I have a six month old black lab who can no longer stay in the backyard while we are at work because he chew and eats everything he can get to, so we have to lock him up in a dog kennel.  Ever since we first got him he has had problems pooping in the thing.  He stays in there for about 6-8 hours a day and poops in the thing.  We are unsure if it is because he is not use to staying in the kennel or if he does it because he is mad at us.  How do we get him to stop?

Answer
I am afraid 6-8 hours are too long to leave a dog in a crate.  Even if he could hold it, the stress of being alone for that long could be causing it.  Can you arrange for a neighbor or professional dog walker to give him a break?  One great solution is doggy day care.