Companies with strong moats that are based on physical assets.

I'm trying to find more companies who's durable competitive advantages come from the physical assets they own. Ideally, these companies are also essential to the functioning of the economy and have an owner's earnings yeild that is greater than 5%. Currently I have been investing in regulated utilities, railroads, and agricultural processors, but I've build up large positions recently, and these sectors are getting more and more expensive. If you can think of any companies that fit these requirements, please share them in the comments. Companies that I am currently invested in: CNI, UNP, CP, AWK, MGEE, ADM, CNH.