I don't feel that on maps like walls (ok, especially walls), mining the entrance and tunnel are all that effective. Now, they CAN be, but if find that the ones in the tunnels are easily disarmed without notice, unless you have someone constantly monitoring them, while the ones in building entrances are very difficult to disarm without notice. Also, the ones in front of your base will be taken out by the first humvee/buggy that cruises in. It might/will destroy him, but the influx of enemy vehicles will quickly remove the possibility of laying mines at your entrance. However, I think you're tactic is legitimate, but I don't think it is so superior to the building entrance method to warrent the latters labeling of "n00b". I find it quite effective, and find that few of the early engineers who attempt to run into my weapons factory make it past the back door.
(I think something we should keep in mind early in the game are the "usual" spots rushers go for...i.e-how often to YOU rush into the FRONT door of the WF at the beginning of the game, or the front door of the powerplant or TR. I think more mines should be placed on back entrances early on...I've found it works pretty well).
Well, there's my two cents.