Dogs only be destructive when they are very bored.
The old saying is that a tired dog is always a good dog.
What kind of food is your lab on? How often does he eat? Kibbles that are not digestible can make dogs poop often. I am not telling you that you should try raw diet unless you are comfortable with it. Dogs are on raw diet tend to poop less.
I would try give him something to chew on while you are not home. It sounds like he is bored at home and it is fun to chew the pee pad. It is something he is having so much fun with. I would try to find something better to keep him busy while your absence.
And.. One more thing I forgot to add. I would try to introduce him back to crate training and get one that doesn't have a room to stand up only lay down. When a dog gets too much movement, it triggers the bladder and bowel to come out quickly. If you are going out for jogging with your lab, all of sudden he needs to poop now.