The butt is a very complex piece of meat. Here is what I suggest: buy a butt and separate it into individual muscles. Everywhere you find a natural separation line, follow it. Don't cut anything other than membrane or where the muscle attaches to bone. Then cook a whole butt and separate it the same way and taste each piece. This will give you a better idea of what you want to turn in and what you want to avoid.
I know this sounds kind of odd, but you will understand the cut much better when you do this. When I started, I pretty much thought of it as a big hunk of meat, but it is a collection of many different types of muscle, some much better than the others. For example, a lot of people like to turn in the tubes (which I believe is what is 'falling off' your MM). Many people don't even know they exist.
