A fellow referee asked me this today, wasn’t 100% sure of the answer, though I thought it was limited only by the length of the pitch.
How many times can you march players back for dissent?
The law states that a second infringement can be marched back 10m, but doesn't mention a third or fourth infringement. In theory you could keep marching them back, but this would be poor management. You could also issue a yellow card for a subsequent infringement.
The Rugby Ref would suggest though that at this point you could call time off, speak to the Captains about your decision and allow everyone to calm down. If players are annoyed about something it serves no good to wind them up further by constantly marching them back. Instead deal with and diffuse the situation.
Remember also that if you do have to march a team back 10m you can march slowly (to allow people to calm down) explaining your decision as you go.
This is all about good management.
The Rugby Ref