Too many term limit proposals are specific to one of the three Federally elected positions: House of Reps, Senate, and President/VP. This creates a loophole that will continue the problem of people staying in office for too long, like the entitled monarchies they resemble.
Instead, make it a blanket limit. No one can serve as a federally elected person for more than 18 years, regardless of where they were elected to. this means they could have 9 terms as a congressperson, 3 terms as a senator, or two terms as president. However, it allows for them to serve in multiple roles, but still, no longer than 18 years.
This means they can be president for two terms, but they have to time it with the 10 years they may serve in other positions. It allows someone to establish a track record and show their abilities, but limits them from ruling as a de facto aristocrat for life.
No one who serves in a federal positions will receive a retirement or any other post-service benefits. They cannot work for companies they received lobbying from, they cannot work in industries they impacted with legislation, and they cannot receive renumeration as “consultants” with companies they interacted with while in their elected position.