My spouse & I try to be explicit with each other about who is good cop and who is bad cop, and switch off. Good cop/bad cop can really be destructive as you say when it's done carelessly or if it pits the parents against each other. We try to use it gently to maintain a united front. For instance, with bedtime on a rough night, we pick which parent will cajole & start things off and which parent will take over if things go south. One's the closer, and if bedtime goes well that parent can actually just sit it out. For us that helps us have more patience, as if tempers get high, parent 1 simply switches out with parent 2, and sometimes that resets the kid's attitude too.

We haven't figured out timeouts at all.