No matter where you put it, it will probably end up moving to a place it sees fit. With this in mine, do your best to cover all of your power heads to discourage the nem from getting caught in it. it can be very devastating. however, you can put it where you like and hope it stays but again that is up to the nem itself. luckily all three of mine stayed where I put them, sort of. Mine are at the bottom of my 40breeder and farthest away from my Vortech MP40. Good luck!