a man is said to have laid a beaver trap when he 'lures' a woman into having sex with him (repeatedly) with the promise of marrying her soon. After his hunger is satisfied enough, the man backs off from his commitment.
(this especially happens in conservative societies of developing countries where girls consider it a taboo to have sex before marriage. Hence laying a beaver trap is the only option for the sexually-starved & commitment-phobic guys. In such coutries, a man accused of laying a beaver trap is booked under the charges of rape)
Ajay: Hey Vijay, I can't believe it. How did you manage to nail that conservative gal ?
Vijay: Ya man, it wasn't an easy task. Finally, I had to lay a beaver trap.