I carry a slipjoint Queen mountain man in D2 commercial lobstering every day. There are some rust spots on the blade that I haven't cleaned up yet and I just oiled the pivot with some Penn Reel Lube that I had laying around, as it was getting sticky.
I took a USA Schrade 96OT trapper on a 14 day trip groundfishing to Georges Bank and it was the only knife I used and it held up just fine. If the knife is immersed in water, just give it a freshwater rinse and some oil in the joint and you should be good.
If you are worried about pitting and it is a new knife, stick it in a potato overnight and get a patina formed and that will help the rust, or give the blade a coat of mineral oil. Traditional slipjoint knives with carbon steel blades and natural material handles have been used at sea for centuries.
If you want to go with a stainless blade, any of the Buck slipjoints should hold up well. I used a 110 lobstering in the early 2000's and it was exposed to sea water, heavily salted brine from the bait, and I had no problems with rust or with the stabilized wood handles cracking. The brass bolsters patina-ed up nicely and the blade needed to be sharpened frequently, but again, traditional knives might be prettier than their tactical counterparts but are tougher than people think. I have no problem putting my mountain man through some rough rough work.