What does Madison prescribe as a way for each department of government to maintain its autonomy?

In order to lay a due foundation for that separate and distinct exercise of
the different powers of government, which to a certain extent is
admitted on all hands to be essential to the preservation of liberty, it is
evident that each department should have a will of its own; and
consequently should be so constituted that the members of each should
have as little agency as possible in the appointment of the members of
the others.