Require petitions that only effect one state to only be signed by people of that state.

In virtually all of the current "secede from the union" petitions you can find many signatories that are not from the state in question. This represents a flaw in the system, as an ad absurdium example would be a petition to require Montana to come under the sovereign control of New York, where New York could easily and quickly gain the necessary signatures due to their high population.