The Executive (President, Veep and Cabinet) must face the people (and risk being voted out) every four years. Ditto the Legislative branch (Congress and Senate). Only the Judicial branch lacks any checks and balances. Lifetime tenure is ridiculous, the elderly DO tend to lose it and the SCOTUS can be stacked so heavily that little can be done about it until those biased judges have the grace to kick the bucket.
Ten year terms (beyond the possible life of an administration), staggered so that no more than one can be up for re-nomination at a time? Expand the bench to ten, and one gets replaced (or reappointed) annually.