Milo has had panic accidents when confined or accidently locked in a new room. We let him outside at least 3 times a day to poop and more to pee. Could it be that your work day is too long for your pup? Is there anyone to pay attention to him while you are gone, at least for a little while? Is there a safe outdoor area where he could stretch and play; or an indoor area like kitchen or bath (with toys and maybe a chux pad for accidents)?
My ideal situation would be a dog door, luxurious outside dog house, and he would be free to come and go. Since we have not hired a contractor yet about the door we are lucky to be able to come home and check on Milo during day. He spends some time outside and some sleeping on the couch. We have a baby gate so he does not have free run of the whole house.