How do I kill adventurers before they attack?

I've been playing through my very first full game as the Byzantine Empire. I've been going along fine, except every so often, I will get a message about a raiding adventurer party wanting land.

How do I get rid of them before they attack? I know I can use the murder plot, but it seems everytime I try it, it never works before he gathers his army (this is with using my Mystikos to increase plot chance).

Sometimes in distant lands, the option isn't even available at all, and I just have to accept him attacking...

I really don't want to take the route of removing adventurers completely. I mostly want to know what options I have to combat against them...