Males have a certain body shape compared to females. Also, when they are mature, males will sing loudly, develop glands in their armpits, and get these really funny muscle-y arms. I've heard looking at the tail isn't always a surefire sexing trick, most of the sites I've seen say you only really know when the boys start displaying their behavior - I've even heard of females getting "glands" for a while before deciding they wanted to be girls for sure. :P Not sure how true that is but I wouldn't be surprised.
My female is more oval/rounded than my male, and also a great deal bigger. Their two female offspring are the same as their mother, although they got their dad's coloration. :) Girls are often better hunters than males. My girls are so piggy, I have to hand-feed all the time just to make sure my male gets food! They miss enough that there's usually stuff for them to forage left over.
Robert Falcon Scott - Red salamander HM plakat
Passed on- Friedrich "Freedy"
Four African Dwarf Frogs - Dorkus, Sporkus, Baron(ess), and Bubbles!