There are ways to manage the coaching box other than a technical foul.
My pregame conference with the coaches is very brief. I maybe say three things. However, one of those things is always to remind the coach that he/she needs to stay in the box and they need to be coaching if they are up. Not only does it let some of the less knowledable ones know the rule, but it also lets them know that the crew is aware of the box and that we will be monitoring it.
If the coach stands the whole time when the game begins, a quick conversation when you find yourself in front of the coach on a dead ball does wonders: "Hey coach, can you help me out on the coaching box? You can stand while coaching, but you need to sit while watching." Say it with a smile. Since it was mentioned in the pregame conference, they know what you're talking about.
There are also some hand signals to use if you find yourself opposite the bench. The "wave-in" signal is almost always greeted with a coach looking down and realizing he/she is out of the box followed by a grin and them getting back in the box. The "wave-down" signal is almost always greeted with a coach immediately sitting down (or starting to coach instead of just stand).
It bothers me when I work a game with a ref who says, "as long as the coaches aren't yelling at us I don't care where they are." IMHO, that's just an excuse for an official who hasn't learned how to ref more than just the 84-feet of court. Managing coaches is part of our job. If you don't monitor bench decorum and keep it under control, you probably will end up with no choice than to give a T. I prefer the preventative approach.
Z