anyone using an air fuel meter constantly on their boat? Seems like cheap insurance running a blower. Do the o2 sensors go bad often since water probably hits it occasionally?

We had CMI weld us a couple bungs way before the water and run both EGTs and air /fuel on #2 and #8 full time.
We found that once you dial her in 4 to 5 oxygen sensors later even when they don't touch water, that the full time EGTs on an alarm work just fine as an added tune/ safety tool as the blown oxygen sensors start getting old after the first few..!
Good Luck!

I have six years on the same one.

I had two summers on one.. and made a pass with my mufflers off and when I idled back to the trailer it must have sucked up water.. put the muffs back on and it was dead. New one has been in this past summer.