Don't do it. I started out with the BARF model of raw feeding and used to get these bones straight from the meat processor (VERY fresh). Over time, we started to see chipped teeth. Three extractions on three different dogs later, I learned my lesson - no more beef marrow bones.
There are much better (and safer) choices out there for a pup. If I had a teething puppy, I might be inclined to offer lamb femurs, but only with lots of meat attached.
If you're going to be leaving him and you want to leave him with a "busy toy", stuff a big Kong (you can get the extra tough ones if he's a big chewer) with some ground meat (and maybe some treats mixed in for interest) and freeze it solid overnight. That will keep him working on it without the risk of tooth breakage.