The way I run PC defense of NPC actions in my BR campaign is to
require that the PC allocate RPs to generic defense categories.
These RPs are allocated by the player every season, regardless of
NPC actions. If the PC suspects an assassination attempt, a
holding contest, or espionage attempt then the RPs spent will be
increased. I do not give hints to the PCs when things are about
to happen to them. If the PCs consistently spend RPs or GBs to
provide for increased counter-intelligence, realm security or
body guards, then most attempts will be stopped before they become
a role-playing scenario. If the PCs is out bid, then I will run the
encounter as an adventure.

I have six regents in my BR campaign and am unable to run a seperate
solo adventure for each regent every season. This method allows
most NPC actions to be stopped early by a diligent ruler, but if the
PC gets lax and allows the RPs spent towards defense to slip in favor
of other things then an assassination or espionage event becomes much
more likely.

John Post