In my many years of consulting to organisations who are actively managing their culture I discovered an unexpected fact. The organisations who were doing it best were doing it with only limited external help, or none at all.
This was an uncomfortable truth, in the days where I worked for companies which made their money selling 'consultant days'. "What, you mean the client doesn't need us!" Building internal capability has to be a top priority for any organisation that is serious about culture. The core drive and strength must come from inside. (My yoga teacher tells me the same thing!)