I use something similar to this;
http://www.usgalco.com/HolsterPT3.as...20&CatalogID=7
The one I have is from a local custom outfitter, but it's the same general design. With a full-size M&P, you shouldn't have any issues with tip-outs. Like any carry set-up, though, make sure you've got a nice belt to go with your nice holster