Install an anticheat, that'll make it a lot tougher if not impossible to crash your server by loading tons of chunks, although if your survival server has /dupe, you can still get cucked by pretty much any lag machine. This guide cannot protect a dupe server from minecart/armor stand based lag machines, it can allow the server to last longer, but these machines have like 50 shulkers wired up into a dispenser, so eventually the entity count will rise high enough to overwhelm the server, just disable spawn eggs, armor stands and minecarts.