..." Asking them to not plunder is asking them to stop playing the game, attack and defense is part of the game design. " .....
When someone is hugely bigger/stronger than you, this is called bullying. If the game does not have any way to prevent this ... if it's not possible to play this game without being bullied, then it's not worth playing.
You can prevent it, but it’s upto you as the city owner to manage your city based on how much importance you place on preventing that. It might take some time to set up to the point where you’re satisfied with the plunder protection but you can prevent plunder.
As long as you have plunderable buildings, set up your production cycles at a time that suits you so you can collect it before they do
Choose buildings that can’t be plundered over ones that can
Buildings that can be plundered:
Goods buildings (from your build menu)
Anything not motivated
Most set buildings
Plunderproof buildings
Anything motivated
“All Ages” buildings: buildings that automatically age up with you. These appear as “all ages“ when viewed in inventory
Crows Nest
Statue of Honour
Great Buildings
Military
Town Hall
Tavern Boosts: I’d first concentrate on building up your tavern before you activate the city shield. That’ll allow you to build the silver back up a lot faster inbetween uses if you really need it at the time
Friends! You can’t plunder friends or guild members. So send them a friend request and maybe they’ll accept it
Defense boosts: This one we could debate all day on whether it’s worth it and to what extent it should be built. Either you go all in or you don’t bother with it at all and rely on post battle protection. Clearly your defense boosts are not yet upto scratch, so you should probably be focusing on post battle at the moment.
Galata Tower: get the prints. Build it. It has a % chance of preventing plunder. More importantly though it gives you plunderproof goods every 24 hrs that you can use