I actually was wondering about this too, because if I want a Dwarf Puffer Fish and his 5g would go on top of the kitchen counter most likely. I don't want my cats harassing it all the time.
I almost fully trained them not to sit on top of the Bearded Dragon Tank though, which is sturdier, but I still worry on occasion if I one day turned that one into a fish tank.
29g: Dagger (Dumbo Veiltail Betta), M-O (Microbe-Obliterator, brown Bristlenose Pleco), 3 Albino Corycats
40gBreeder: Cousteau (Doubletail Plakat), Midge & her 5 babies so far... (Guppies), Nimbus (Albino Bristlenose Pleco), Rabbit (Yellow Mystery Snail), 7 Neon Tetras
2 DSH Cats: Rowan & Jacob