Alternators require clean cold air rather than rocks small animals and mud, in extreme conditions I've ducted filtered ram air to them, fit a cheapee temperature gauge to it and when its getting hot say ~ 100- 110 degrees C as the stator varnish and enamel has different temperature capability depending on price and usually are good to ~ 120 degrees C. reduce the load, or install a resistor you can add via a switch in the field circuit. One aftermarket regulator [ balmar ] I've fitted in hot and marine units have a temperature sensor fitted to the alternator you can program the regulator to fold back [ reduce output ] automatically by an adjustable amount when they go over an adjustable temperature. They are not designed to be a trash pump. Some high end Bosch units are water cooled so they can operate in harsh conditions
I suggest if your starters are dying due to water then run a 2- 5 psi air pump into a tank and a tube into the starter brushes end so its kept at positive pressure and the tank will help if you submerge the starter in a hurry when hot. some old school starter run an intermediate bracket or plate with a seal at the drive end so they can run in a wet clutch. that may be an option.