Good idea.
Got proposal wording?
Something to the effect of:
Congress shall not own or manage any land area within a state or territory greater than ten percent of the total land mass of that state.
Lands in excess of the limit shall be returned to the ownership of the state. Congress may enact such laws as necessary to return such land to the state.
Tribal lands shall not be assessed either for calculating the ten percent nor calculated in the total lands of the state.