If your split rings are doing that, reverse the pin so that it faces the opposite direction -- usually this solves the problem. Also, make sure you're pedal position is sufficiently extended so that you're not slamming the fins up against the boat -- it will not diminish your speed or capabilities.
BTW, all the current (and recent) masts spin off with an adjustable (Crescent) wrench; Vice Grips also work but can scratch the mast finish, abrading the fin; pliers usually don't have enough grip. If you do replace a mast on the water, remember it may un-thread spontaneously without Locktite Blue in as early as a few minutes. Teflon tape will work as a temporary substitute for Loctite (and may be a consideration for your emergency kit). Split Ring pliers are a great tool to have if you're trying to replace the rings on the water. Finally, don't forget that the Mirage Drive DOES still work with only one fin, although at reduced thrust obviously.