This is a concern for our family because we move so much and buying a new house with every move isn't an option.What I do when a potential landlord asks if we have any pets is that I tell him we only have pets that live in glass tanks. So far, that has been a very satisfactory answer because as a landlord, their primary concern is animals that may damage the property (ie cats and dogs) and they rarely have enough imagination or care to consider what might actually be living in those tanks.
Now, this is for renting houses. Haven't looked at apartments since we were newlyweds. But it works so far. I don't even hide them if the landlord comes into the house for some reason because we've signed a lease that does not specify that we can't keep certain animals except cats or dogs and they can't do anything about it at that point.