Aquarist's intuition. I thought, for some reason, to go check out the aquarium. I found my sea hare with it's head completely sucked into the inlet vents of my Seio 1500

I unplugged it right away and took the powerhead (with sea hare stuck in it) out of the tank right away, because I understand they can possibly kill everything in the tank if they die?
The prognosis was not good. It was heaving and pulsating slowly and exuding the white slimy stuff they exude when they're stressed, as well as some snotty looking stuff. It was quite foul, actually. Long story short, the guy slowly wormed himself out and seems to be perfectly fine.
Is there any way to sea hare proof the powerheads?