if you lose a plunder attempt you have to pay 10 ingots to plunder again and if you lose 3 times you are done for.

Anyways there's a better way to avoid being plundered.

If there's for real only two groups in your server then your group can sabotage on purpuse their plunderings.

How do you do it?

Warn them that if they don't stop doing it then every single person in your group will stop running SS convoys.

If you do it for 2 weeks you'll see they'll begin to plunder their alts and so they'll stop plundering you.

Given your power could be running 40 coins convoys isn't at all a bad idea (since you have equipment and eight inner gates to level up).