The whole point of attempting this is to allow these difficulties to force you to decompose the system further than you would using the larger building blocks of MVC.
About six months into working with Rails full time, I began wanting a third place for my logic. Controllers were suboptimal, and models weren't always right. Coming from a native apps, I felt restricted. I later learned that POROs were well and good. But I doubted myself because the Rails way says little.
I'm good with POROs (assuming Plain Old Ruby Objects). I'm a huge fan of Domain Driven Design. My issue with the parents is that without going into what many Rubyists would call Java-land, one would find it hard to separate concerns. Also, I don't agree that an MVC can truly be fully decoupled from the V. This is why one seldom has one MVC to rule them all.
About six months into working with Rails full time, I began wanting a third place for my logic. Controllers were suboptimal, and models weren't always right. Coming from a native apps, I felt restricted. I later learned that POROs were well and good. But I doubted myself because the Rails way says little.