ROCK THE BOAT means disturb a situation that is satisfactory and stable otherwise. It means to cause trouble when it is not welcome at all.
Some people are really good at ROCKING THE BOAT (I am sure you have a couple of friends like that). So you can say:
- Tim is really good at messing things up by ROCKING THE BOAT.
Or if you actually mean the opposite, you might say:
- I totally trust John. He would never ROCK THE BOAT unless it was absolutely necessary.