See - the intakes DO have guards on them, they're not open - and the guards are VERY small. I'm not talking mesh thin weave guards, but very thin guards... no guards would probably mean that I'd have mushed anemone in my tank
The only thing that might have prevented it would be to do a super fine mesh or sponge/quickfilter type thing - which would be another thing to fight with in regards to nitrates...
Unless there's something I'm missing?