Boots, sorry you had to resort to puddle notes to get your Dad's attention, but sounds like things will be under control soon.
See if you can talk him into trying Worlds's Best Cat Litter It's a little spendy but if Dad will scoop out the unmentionables a couple of times a day, he'll find the remaining litter doesn't collect odors. I've even sniff tested (very carefully) month old litter and there is NO catty odor. Good luck with old Dad!