I understand what you mean about "the key thing...to a stranger" (even if bonded, its a hard thing for me too). what about one of those "dog doors"?, the kind that fit into the sliding door, if you have one.
as for what someone said about not leaving them water...OMG! LEAVE WATER PLEASE!!! and the comment re if they have diarrhea, that they "crate" them and someone comes in mid-day, or mid something. !!!!! awww c'mon. I would think for most of the time, dogs aren't sick..if they are , then block off a section of house or garage (if its cool there), but confine them w/ possibility of diarrhea episodes??? I feel sick.
off the soapbox now. I had an older dog that I put thru this. 12 hr shifts definitely can turn into 14. I put out the water, a few snacks...toys, papers on the linoleum floor. --and worried like crazy. this dog never used the papers...and she never did anything elsewhere. she waited, I came home in the very early am...and we would go for a walk, in the dark, she made it short and quick...ok, actually about 10-15 mins..but I call that short for a dog who's been in the house that long. we always went for a walk on the beach before my shift, and for longer on my days off.
she was hmmm, about 11 yrs old at that time. (just for bladder info, lol).
she's gone now ;-
good luck, hope you make the right decision.