Hmm seems like he likes the outdoors. Maybe you could invest in something like this...
PET-A-POTTY ONLINE STORE_The Original Dog Potty_Small_dogs_to_large_dogs_PETaPOTTY_The Pet's place of business http://www.portabledogpotty.com/
Something along those lines, I think it would help.
Do you have anyone who could come over in the afternoon to let him out?