How can I relieve sciatic nerve pain permanently?

Cure, Unlikely... Sciatica can be managed effectively and can be relieved in a vast majority of people, but it will always require diligence on your part for nsaids, exercise, stretching and weight control/loss. For those still having issues it may require treatments (injections, surgery, etc) to maintain relief as well.
Manage causes. Sciatica usually result either of trauma or misalignment of spine (either subtle or major). Omt from osteopathic physician (aao or cranial academy online). See your doctor for short term pain relief - then go after the cause as this usually recurs over time. Long term: omt, yoga, tai chi, feldenkrais, alexander technique, bowen and other bodywork along with core strengthening - after alignment.