Secondary to this, Ice Guardians (documentary about enforcers) is on Netflix now, just saying. Getting word out there as far as skilled veterans go ... early on there is props in comparison between Gretzy and Crosby, noting with a good enforcer how many less concussions would Crosby had suffered (or how better he would be) to date. Maybe with Reaves, Crosby will play a full season this year.
Neither Dave Semenko nor Marty McSorley prevented Gary Suter from running Gretzky into the boards from behind, starting what became a long history of back problems for the Great One.
Sidney Crosby's first concussion comes from a hit by David Steckel. The video shows (to me) that Steckel tried to avoid him, but ended up running into Crosby's noggin. No penalty called. And then, later that year, Victor Hedman hit Crosby from behind against the boards, but in the numbers. Crosby left and never returned that season. Neither Steckel nor Hedman are known for being dirty players.
The theory that enforcers will serve as deterrents to dirty players is sort of like saying that having a handgun will deter a person from shooting you from behind: the dirty player has already made up their mind to hurt you, and will not be deterred if your enforcer isn't sitting next to you or he doesn't care what the consequences are.