Cooper is 7 also and a indoor dog, I have found that smell can have alot to do with what Cooper eats. Seemed odd to me but changing his dog food helped loads. For dirt on the underside and just cleanup I use uncented baby wipes for sensative skin. It's been about 4 months since his last bath however it's time. For a while he got them once a month now with the diffrent food it's about ever 4 months or so, or when I just can't get him to get out of the tub. He has a habbit of jumping in if you let him in the bathroom and just standing there looking at you with that wash me look.