Your rosary is a weapon, so why not have it blessed?
Can. 1166 of the Code of Canon Law states,
“Sacramentals are sacred signs by which effects, especially spiritual effects, are signified in some imitation of the sacraments and are obtained through the intercession of the Church.”
When a priest blesses a rosary, it becomes set apart as a sacramental object for the service of God. During the blessing, a priest may pray:
"Through the prayers and glory of Mary, the Virgin Mother of God, in remembrance of the mysteries of the life, death, and resurrection of our Lord Jesus Christ, let these beads of the most holy Rosary be blessed and hallowed."
Typically, the priest will then sprinkle holy water on the rosary.
Here is Father John Paul Mary, EWTN Employee Chaplain, blessing a rosary:
Now, your rosary has been dedicated to a sacred purpose! This blessing reminds us that our prayers are united not only with the Blessed Virgin Mary, but also with our brothers and sisters across the global Church.
As Pope Leo XIII once said of the rosary,
“(The Rosary) is the remedy for all our evils, the root of all our blessings. There is no more excellent way of praying.”