It's simple. Every ten years we have a state by state referendum on whether that state wishes to remain part of the union. Perhaps there would be a supermajority requirement. Nothing would be better designed to restrain impulses toward activist or extreme policies by either party. Go too far and suddenly you only have 45 states or whatever. In fairness, there would have to be a mechanism to account for accrued but unpaid entitlements, eg social security, and outstanding federal debt. Maybe just zero them all out and call it even. In the event of secession under this Amendment, real property owned by the federal government would revert to state ownership. How would you vote, if the referendum were being held today?