Well...you really shouldnt be keeping your dog alone for that long....but if you MUST...i would suggest you get a pair. Not necessarily the same breed..but essentially they must have a companion.
I have a Dane and a Lab...my work keeps me away for 8-9 hrs everyday....So i leave them with tonnes of toys & chewies and once i am back...i ensure i spend good 2 hrs of quality time (walking, playing or maybe just lazing around with them). Trust me..they are doing okay...thankfully!!!