Poor dog, he is geriatric, he cant help it things are not like he was 5 any more. Its not the pups fault. Tell the neighbor kindly, that he might have to persue other options, that you will need to charge him more for more frequent trips one or two times isn't working for the pup. he can not control movements for 2 outings through out the day. Poor Fella, Dont take it out on the dog, I know its frustrating. The dog probably gets upset when he has an accident in the house. If old fella is in that situation and is only messing on a particular rug it might be worth it to get some plastic to place under the throw rug and slowly move the rug to a non carpeted floor area. For the just in cases. As for being a good neighbor there are limitations, When I pet sat I would rinse and leave outside in a bucket or bag and over the clothes line and let the owner take care of the rest. Good Luck