What can be done to protect the players is limiting the number of contact training sessions they can attend, and also limiting the number of games a season each player is allowed to play.
Another option could be to seriously limit the number of substitutes each team is allowed to make, as this will mean the players will have to be fitter and therefore not as big, and hopefully this will reduce the impact each tackle will have. However Rugby League is also having to deal with head injuries and that game requires a lot more fitness than Rugby Union.