John, this may be the source of the quote from Proudhon:

...."To return once more to the fundamental idea in this work-this is how property, by creating guarantees for itself that both spread it more equally and establish it more firmly in society, itself becomes a guarantee of liberty and keeps the State on an even keel."...

This is from Selected Writings of P.J. Proudhon, Anchor Books Edition, l969. p.133
>From a later writing of Proudhon entitled "Property", 1863-1864

Roy Davidson