My first K&N filter was put on a MX bike doing short circuit racing, so as for dust, mud, rocks, water, other bikes and nearly anything was tossed at a totally exposed filter with no problems, clean it after the days racing and your good to go next week, once a month a new piston and rings, little end bearing and pin, then your good to go, no problems just trophies.
But in those days it was just normal to use a K&N filter, clean it in either lawn mower fuel or excess racing premix poured from the inside then soaked in any container around and all was good to go, no big deal, that was just the normal G O.
But that was only ridden on sundays by a total lunatic with a death wish and at full throttle most of the time, plus add the odd tune up down the street when no one was watching during the week, all was cool.