I wrote here about our cat problems and how I had a pet behaviorist come out to the house for a consultation. The primary things we concluded were that Dodger likes to go out in the open where he has infinite escape routes should his little brother decide to come stare at him and that there was a possibility that the cats didn't like their litter anymore. She made a few recommendations: move all the boxes back upstairs to the cat room, add another box, put at least one box right in the middle of the room, and replace the litter in a couple of the boxes with potting soil.
After some time, I determined that Dodger was not at all interested in the soil and that, although Oliver would use it, he didn't seem to have a significant preference over the clay litter. I would eventually switch those boxes back to the litter we used to use for the first 3-4 years of the cats' lives, which is a corn-based litter. We had switch from the World's Best Cat Litter to Cat Attract at some point after Dodger starting having problems. At the current time, Dodger again has little interest in the corn-based litter, but Oliver will use either.
After replacing the carpet on the stairs and moving all the boxes to the cat room, we no longer had a problem with Dodger misbehaving. Oliver was another matter. In fact, he suddenly got worse, peeing in the living room and dining room. Every night, I would walk around the dark house with a blacklight to figure out if and where he had been bad that day. Due to the sudden change in behavior from Oliver, I took him to the vet. She didn't find anything obviously wrong with him, but had me bring him back a couple of weeks later for stomach x-rays, which turned up nothing. Having ruled out health problems, I emailed Mary again to schedule another visit.
We walked around the house again, with me pointing out all the areas of Oliver's transgressions. I described in detail his changes in behavior, including both the peeing and the fact that he no longer sat on my lap and snuggled in the evenings like he used to. After all this discussion, Mary said, do you think he just needs a little box down here? One of the key pieces of information seemed to be that, much of the time, I caught Oliver in the act of misbehaving; he was in the living room, hanging out, and instead of climbing upstairs to use the litter box, he would just pee on the floor. I was hesitant at first at the idea of putting a litter box on the living room/dining room floor, as I was afraid that Dodger would then start going on the floor nearby, as had been the original problem with having a litter box in the powder room. I also knew Zach would hate the idea of having a litter box anywhere out in the open or near where we might eat. However, after some more talking it out with Mary, we came up with the plan to put a tiny litter box that Dodger could not possibly fit in, filled with the corn-based litter that Dodger doesn't like, in the corner under Oliver's cat tree where Dodger doesn't like to go.
The next day, I went to Target to buy a tiny litter box. I had the dimensions of the cat tree base where the box would go. I was planning to get a small storage box, but ended up finding a silverware box that was the perfect size.
It's been over a month since getting the new tiny litter box. Since then, Oliver has only had one accident, and that was because I failed to clean his tiny litter box, so he went on the floor right next to it. So as long as I keep on top of cleaning Oliver's special box, I think we're going to be happy cat parents. I am so relieved to finally have this under control. It had gone on for so long, and I had tried so many things before calling in Mary. When I first got Oliver his special box, I was still checking around with the blacklight every night. Not finding pee seemed so improbable, it was hard to believe the box was actually working. I didn't want to get my hopes up at first, but it's been long enough now that I'm willing to call this solved.
I'm so grateful to Mary. While, in the end, her solutions seem pretty simple, I couldn't have arrived at them on my own. For all the Internet research I had done, all cats are different, and things get more complicated when you have two cats, each with different preferences. It seemed like whenever I'd make a change that was better for one cat, things got worse with the other. Now we have two happy cats and two happy cat parents! Thanks, Mary!