the "train tracks" is always the worst. I'm sure we all know the open-ice hit can be deadly, so I'll share a few stories from when I played competitive minor league hockey...
One of my first bodycheck games in peewee (when hitting started in Alberta), I took an elbow to the gut when attempting an open-ice hit. The guy dropped int oa crouch, and lunged for my midsection. So, if you want him to avoid being sprawled on the ice, breathless, then make sure he keeps his arms low, protecting his mid-section, and lead with his shoulders...but also remember to keep a low centre of gravity. He'll make an instant impression, if he wants to play that physical Peca-style of play.
Second story was a head-to-head open ice hit. Both of us careened straight at each other, and both of us hit hard enough to topple us several feet in the opposite direction, and i sent my mouthgaurd flying, banging around in my helmet. So, get him to pay attention to angles, since head-to-head is going to hurt both parties.
That's enough of open-ice hitting...
scrums along the boards are chaotic, but there is a method to the madness. A pin is simple...don't pin the body, pin the arms. Skate in at an angle, and press the body around the elbow region. The opponet will be stuck and he can take control of the puck without moving from that position. That's a great rub-out. Oh, and keep the fists out of it, nothing good ever came out of a fist-leading bodycheck.
Taking a hit has already been covered, but hitting from behind is a no-no, for obvious reasons. I nearly broke my neck a dozen times from hit-from-behinds, both accidental and intentional. My last year of hockey alone I recieved four of them, three from the same player. So, best advice? Don't let the kid become a real jerk, and keep it professional. Once it gets personal, that's when hitting from behind becomes an issue (outside of the usual accidents).
Hopefully I've been helpful, on some level.