Rock obsession

Mr. 4 is current obsessed with rocks.  He picks up every one he sees and his pockets - jacket, pants, sweatshirt, and he as even tried to sneak a few in mine.  This mean his jacket always weighs a million pounds and his hands are always filthy.  We've tried to hold to a "no rocks in the house" policy but he does his best to sneak a few in at every opportunity.  We finally gave him a yellow bag to store them in that must be kept right by the front door.  So now guess what goes with us wherever we go?