We have gavelkind as well, which meant that when my first character died, it split the realm into a vassal countess and a duchess. Then, my character had a son! Woohoo, inheritance through males first!
So I thought, I should kill this countess and take back my land, being next in line. Unfortunately, she passed away from illness before I had a chance to just knock her off. So now I have Demense 2 again, and I'm starting to press my de jure claims against the rest of my duchy of Ulster, while still being squeaky clean. Though, piety took a hit as there's a crusade going on. How can I worry about that when there's so much to do locally?