I have three box turtles - two females and one male. I must have a particularly adept male, because during breeding season he manages to "get with" both females several time a day. Nothing clumsy about it, although there are times when the females do try to wander off on him - or rather, out from under him.
Actually, he uses the claws on his hind legs to grab the shell of the female, and hangs on for all he's worth. An unco-operative female can close her shell up tight enough to not only make penetration impossible, but also to seriously pinch his toes. I've had to separate them by placing a screwdriver between her uppper and lower shells and twisting it just enough to get his little tootsies out.
I get eggs quite frequently; the only problem is all three turtles view them as a delicacy.
In most turtle and tortoise species, the male's lower shell is slightly concave to accommodate the convex upper shell of the female. That's one way to tell the sexes apart.
And, yes, male turtles are hung like Spaw claims to be. Not a pretty sight!
Contrary to popular opinion, almost all turtles and tortoises can right themselves when they end up on their backs. The biggest danger is if it's extremely warm or if in direct sun, they can overheat and exhaust themselves trying. I'm surprised a zookeeper would claim they can die that way.
campfire (also a zookeeper)