How can you tell if a gecko is a girl?

The easiest way to sex a leopard gecko is to check its underside. If it has 2 bulges at the base of the tail and dark spots a little above the base that looks like a triangle without a base than the leopard gecko is a male. If there are no bulges (which are called hemipenial bulges) and you cant see the dark spots (which are called preanal pores), then the leopard gecko is a female. There are also people who say that males are longer and have bigger heads, while females are smaller with smaller heads, but there isnt enough proof to say that that is a true fact.