But we need some context, because as far as my knowledge goes, castles were not takeable in most of the situations at all, like Constantinople, for example, was surrounded by turks for around a hundred years but until active use of bombards started it was not taken, and this is just one example.
You really think that around 100 people on one server is an unachievable goal in case of your Game?..
No, not really, even in Minecraft 100 kilometers is usually enough on an anarchy server for a base to be never ever found, and this is Minecraft with it’s small height limit and ability to actively wallhack, and since your game code will not allow for wallhacks, a man can just dig deep into the earth if he wants to feel safe.
Eehh, more likely for this kind of purposes a mod will have to be done, because if breaking everything is super-easy in your game, then just disabling chunk claiming will not work as fine as i imagine it.