You want people to pray the rosary in the sanctuary?  The sanctuary is reserved for the Mass and very few other things, not private devotions.  Typical practice is to stay out unless one has good reason and then to enter with the utmost reverence.  And, whether the altar is freestanding or built up against, the wall the space is ill-suited for devotions.

I can see praying the Rosary at the sanctuary rail, if it is present, but not in the sanctuary.  And I can't think of a church where praying private devotions in the sanctuary is allowed.  Keep it in the nave.