there have not been reports of assassins taking down nerites as the nerites can seal up very tightly. This would be a poor solution. If you don't want your nerites, rehome them. If you don't like the poo, get a turkey baster and suck it up at feeding time inbetween water changes. i don't think nerites are excessive poo'ers, just efficient eaters.
As I realy want some when I get my 75 set up