My own preference would be to move the intake farther back (but not so far back that the props cause a problem) and to use a forward facing scoop (if it isn't what is there now) to give it some assist and avoid any suction when the water is passing by fast.
Basically, I'd want to locate the intake away from air, protect it from suction, and give it some help getting water in to widen the tolerances.
Adding things like valves and air traps may help, but my own preferences is to avoid adding parts. There is an old saying in software, "Novice programmers add corrective code; experienced programmers remove defective code." Increasingly, I've been trying to apply the idea, a.k.a. "The KISS principle", to my boat.