Filter question?

[Dirty Fish]

I currently have my African lungfish (Annectens) "Clayton" in a 77 gallon filtered by a Fluval 404 canister. If you're familiar with the exhaust head on this particular filter, you'll better understand this post. My problem is this................ On the filter exhaust there is a rounded bottom part that can pop off for cleaning, well Clayton must have thought it looked tasty because I woke up one morning to find it totally chewed up in his sewer pipe decoration. I put a new one on and even siliconed it in place, and he ripped that one off as well. It sucks because when he does this I lose all surface agitation. What kind of filters do you guys and gals use? By the way I understand that a lungfish does not have traditional teeth, but rather tooth plates for crushing, but you should have seen the damaged filter part. It looked as though something with very short, very sharp teeth munched on it.