I know there has been some cases where a flight instructor is sued after a current or former student does something that gets themselves (the student) killed or causes damage.
I know that there have been cases where a flight instructor has been acquitted by proving that they took due care in their flight instruction, and the accident was not a result of poor instruction.
What specifically would a prudent flight instructor do to ensure they are keeping detailed enough records to prove that they are providing adequate instruction and that a resulting accident would not be due to poor instruction?
What are the records a CFI is legally required to keep, and what are the records they should keep in addition to that?
This question is in context of CFIs in the United States.