The extreme solution disconnects the current gravity sewer pipe between the street cleanout and your house. There can be no sanitarty sewer backup from the street because there is no pipe for the backup water to get to your house.
A Ginder Pump system is then installed. All septic waste enters the grinder pump basin where it's emulsified and discharged under pressure into the verticle stack at the street. The discharge pipe is only 1-14 inch in diameter and enters the stack at only 5 feet below ground level, at a much higher level than the extisting gravity sewer pipe, and has an inline check valve backflow preventer. (Costs range from $10,000 to $19,000.)
A similar solution can apply to the storm sewer.