There is no place in the Construction for secession because it was never intended to be allowed. If you want proof read The Articles of Confederation.
Article XIII of the Articles of Confederation seems pretty clear to me.
"And the Articles of this Confederation shall be inviolably observed by every State, and the union shall be perpetual; nor shall any alteration at any time hereafter be made in any of them, unless such alteration be agreed to in a congress of the united states, and be afterwards confirmed by the legislatures of every state."