We count (though we use A,B,C as opposed to numbers).
Center always identifies the "Ace" defender, the Playside A gap defender. DLM are always "counted" before stacked defenders. We always consider a 0 tech Nose to be the "ace" but we never count a stacked Mike Playside, he is always backside (-1).
Then we give the kids 3 rules.
PLAYSIDE
1. Identify YOUR defender and call/point him out.
2. If your defender is on or near the LoS, target Playside #.
3. If your defender is off the LoS, find the "nearest ear" and double team that defender.
BACKSIDE
1. Identify YOUR defender and call/point him out.
2. If your defender is on or near the LoS, target Playside #.
3. If your defender is off the LoS attempt to double team the first defender to your Playside.
Basically, on the frontside we will sometimes have a double with the center and guard on an 1 or 2i tech "Ace" but we will never get a guard and tackle double on a backside 3 tech.
We also add another permanent rule to our "uncovered" guys (the ones who identified their defender OFF the LoS, we don't use the terminology "uncovered") NEVER CHASE a defender, if a defender is slanting away from you, continue to second level.
We tell our "covered" players that they have to maintain the block on their defender through the play NO MATTER WHAT. Slow Oklahoma is a great drill to instill this concept.
If (and that's a big IF) we get VERY good at this we will eventually start teaching our "covered" guys to come off of the combo when the player slants backside. We have only don't that once with a advanced few lineman.
So who blocks the LBs? Our backs. If we are in a single back set, our ball carrier reads the LB to determine his running lane....hit the frontside A gap full steam (he best but is no cut), if the gap gets clogged by the backer, jump cut to backside a gap.
The key is finding the right kid who can determine which gap to take without hesitation.