if you are going to grow it for breeding, get it away from the other plants!!! like far away, different room, different part of the house. pollen can just float around in the air.
random pollen floating around can land on your females, pollenate them and you are fucked because all you have is a crop of seed plants.
if you dont plan on breeding- kill them as soon as you know they are male. then use the plant material for hash.
you cant see a tiny bit of pollen that could be floating around and potentially pollentating your female flower.