Before discussing about remedial measures for Pitra Dosha, one has to understand the Karma Sindhanth, and different types of Karma. The Karmas that have become necessitated for the current birth is known as Prarabdha Karma. Sanchita Karma and Aagami Karma can be destroyed by the fire of wisdom but experiencing Prarabdha Karma is inevitable. However, by improving ones mental strength, its effect can be felt reduced.
Without doing good service to parents, in their livehood for which one is bounded, there is no much importance in remedial measures after death. However, with dedication and devotion to God and prudentness of own deeds, any remedial measure would ultimately do good to the individuals.
Make it a practice offering good service to the mankind without any expectation in return regardless of Doshas of any kind you are having. Need not have to bother much about astrology and remedial measures. Concentrate on good things to be done only with devotion and dedication to the God you may believe in. Trust and Behave with believeness in your own Karma honestly.