A tool for fastening fencing material to a post with a staple. The tool includes a base plate; first and second handles; first and second crimping arms, and a cam operatively engaged with the first handle. A slide is operatively engaged with the cam. The first and second handles and the first and second crimping arms are pivotally interconnected and attached to the base plate so that when the first and second handles are pivoted towards one another from an open position, the cam advances the slide, which advances the staple so that the crimping arms may crimp the staple to the fence post. A method for attaching the staple to a fence post is also described and claimed. An inventive staple is also disclosed.