UM Secondary play

The UM secondary this year is playing leeps and bounds better than last year, but I also have seen very clearly that Louis and Peppers are doing far more holding and grabbing than I have ever seen before. As the Indy game showed, the refs do not seem willing to call it even when it's obvious. Does anyone think this was something that was actually thought to the DB's ? To go ahead and be far more physical because the odds the refs call it are very low? It seems to be a very effective method. I'm not knocking it, don't get me wrong. I have watched all of UM's games this year and I have watched Louis especially hold, interfere, and never seem to get called for it. My question is do you think that this idea of going out there and being overly physical was something that was taught? That over the long haul the DB's will foil far more plays than they will be flagged for? Seems to be working very effectively.