One story tells of St. Patrick standing on a hill and using a wooden staff to drive all the snakes into the sea, banishing them forever from Ireland. An exciting idea and I have no doubt that if one is empowered by the Holy Spirit this could actually happen.
Although it's true that Ireland has no snakes, this probably has more to do with the fact that Ireland is an Island and snakes can't get there unless brought in by soneone.
It is believed that the story of St. Patrick and the snakes is most likely a metaphor for his bringing Christianity into Ireland and driving out the pagan religions. (Serpents were and still are a symbol of evil)
The staff, or rod is a symbol of authority. So I believe that St. Patrick used the authority given him by the Lord God, to drive out the pagan religions (snakes).
Interesting, isn't it.