Using a four-leaf clover as a shamrock is another example of how honoring St. Patrick has lost its original meaning. March 17 was once a religious holy day, not a holiday.
The shamrock is a native plant in Ireland, used by St. Patrick to explain to the pagans the Christian Trinity -- how there can be three people in one God, as there are three leaves together on a shamrock stem.
Unfortunately, celebrating St. Patrick's Day for some is an excuse for rowdy behavior. Substituting a clover for a shamrock is in keeping, after all, with the present culture and demonstrates how secular the day has become.
I'm sure St. Pat would have no objection to controlled celebrating. The Irish are a fun-loving people.
Just remember the history of the shamrock, and don't substitute a clover.