Lord Thane
Really if you want to make it harder (notice I do not say impossible) to castle pass, if less than 20% of total army is home, reduce protection. If you're clearly not even trying to defend, why get full prot? 3 is extreme, but maybe you only get 9. We need some chaos in protection times otherwise it's attack once a day to keep the enemy away.
What about straight up matching CLI and Protection time defender. I only get 18 hours, they only get 18 hours. I get 24, they get 24. At 9 and 9... that's attacking pretty darn often.
Maybe just make protection always random between 20 and 24 hours.
Careful it adds this layers of strategy and mindfulness to the game. Many people have shown to not like that. CLI protects from 3 ticking someone, so don't have to worry about that anymore.
These thoughts brought to you by: I just woke up.