I second the crate advice - great for both toilet training and keeping him and your house safe.
I don't remember how young he is; if you feel that he's too young to be crated for the 4 hours that you are away, take a look into setting up an exercise pen around his crate - in the kitchen or bathroom so there's no carpet to chew
and with the door left open so he won't feel trapped.
Here is a webpage with better explanations than mine and even pics
http://www.dogstardaily.com/training...-amp-doggy-den