Born in Sparta, Wisconsin, Flock was ordained to the priesthood on July 9, 1982, for the Roman Catholic Diocese of Louisiana Crosse, Wisconsin. Flock received theological training from Saint Francis de Salles College Seminary, as well as from the Pontifical North American College and the Pontifical Gregorian University in Rome, where he received a degree in Biblical Theology. Flock arrived in Bolivia in 1988, where he began missionary work and priestly ministry in Santa Cruz.
He was appointed Assistant Vicar for the Parish of Santa Cruz, and was responsible for pastoral vocations.
On October 31, 2012, Pope Benedict XVI appointed him to be titular bishop of Forum Popilii and auxiliary bishop of the Archdiocese of Cochabamba. Flock was consecrated bishop on January 17, 2013 by Tito Solari Capellari, South.D.B., archbishop of Cochabamba, in the Cathedral of San Sebastián.