The collective might of society. The only natural right is "might makes right". Every "Right" we grant ourselves after that is simply a particular implementation of that initial principle. The key is to make sure your group of like minded folks have might on their side.
A right necessarily entails a responsibility onto others. Without some framework of mutual agreement and enforcement, talk of rights is utterly impotent.
Within the framework of a society, whatever rules have been defined are law. Structuring society in such a way that minority rights are protected is a part of this. One doesn't have to reference some overarching 'natural rights' to have them protected: you simply write them down as one of the founding principles of your society. This is what the declaration of independence/bill of rights has done and its worked out pretty well so far. A right is always a reference to a constraint in behavior, agreed upon through some mutual framework, and enforced through the might instilled to that framework.
But make no mistake, any of these "rights" will always be at the whim of the majority. The question simply becomes how big of a majority is required, and how well can your institutions withstand a serious attack on the minority by a (less than supermajority) majority. Speaking of "self-evident truths" will not save you in the face of such an assault. We must always be vigilant that the structure of our institutions are sound.
Laws merely define approach to Rights.