Pet Sitter Job in Somerville, Massachusetts

I have a 4 month old terrier mix puppy who normally comes to work with me. But I commute into Cambridge once a week on Thursdays for meetings at another work location where there is no option to bring him with me. The pup is very well socialized with people and other dogs. He is also well house trained. However, he is trained to go on grass. He stayed one Thursday with a friend in the Cambridge area and he had a few accidents which were likely due to the combination of no available grassy area outside, and the other dog he spent all day playing with. He needs his downtime/naptime. Most work days he spends a majority of the time napping under my chair. I'm looking for a semi-regular place for him to stay while I go to the office in Cambridge on Thursdays. The hours could be fairly flexible, especially for the morning drop off which could be anytime between 7am and 10am. The evening pick up would have to be after 5pm. The ideal location would be within walking distance of Union Square. A grassy yard is a big plus, or nice dog-friendly grass areas for walks that are *not* near busy roads as he is not good at walking near traffic.