Sin bins for professional fouls only and if the team with 13 scores a try at any point within the 10 minutes the binned player comes back on. This makes sense as a try or penalty try is already considered a harsh enough penalty in instances where a professional foul occurs but a try is still awarded.
Bring in a "ejection" rule for serious foul play where the player is disqualified but the infringing team still plays with a full compliment. This will not lead to players purposely taking out other players as the media would have you believe and this can be seen in AFL, NFL, NBA etc where there is no concept of teams being forced to play a player down.