The sabotage function can be easily abused by someone who's multi-accounting as he can sabotage all of your castles for as many times as how many accounts he has, all in less than 1 minute per account thanks to the 3-second travel time using feathers.

I'm a lvl 70 player who have been constantly sabotaged by a player using 6 different accounts over the past week.

All of these accounts are fake lvl 70+ accounts maintained by a player whose real account is unknown to me. The fire damage you get from 6 50% sabotage missions is somewhat comparable to the fire damage caused by defeat in battle, which is annoying.

So, here's the problem. I just have no way to defend myself against these sabotages, even if I build guardhouses the dude would just keep attempting a sabotage until he gets successful thanks to the 3-second travel time using feathers. And even if I burn all of his castles to the ground (as I already did) he won't get affected since, again, they're all fake accounts.

My suggested solution is:

If the travel speed of a sabotage mission is capped at 25 for example, it will cost much more time to do a sabotage mission than it is now, even using feathers will not help much. This would give guardhouses more value as you would need more agents to successfully sabotage a target, limiting how many targets you can sabotage at a time. This will ensure that sabotage abusers will have to commit a serious amount of time to actually sabotage and hopefully stop their abuse. This will also make having guardhouses meaningful as they would be useful in deterring such abuse.

TL;DR: Sabotaging must be reworked so that it requires much more time than it is now.

I don't see how this would punish players who are following the rules. It would only make sabotage a slower process and they would still be able to do daily tasks and harm players. But it would make sabotaging abuse extremely difficult compared to now. If an abuser wants to sabotage my 7 castles (4 green, 3 kingdoms) and an average of 30 mins is required per trip, then 1 mission will be 1 hour (30 mins going + 30 returning) and he would need a minimum of 7 hours to sabotage my castles assuming all of his attempts were successful and more than 7 hours if they were not.

And again, people doing daily tasks won't use feathers just to sabotage a nearby enemy. It's just not worth it.

I can only see abusers suffering from this.