Modes defined with define-minor-mode have hooks.

C-h v visual-line-mode-hook

    visual-line-mode-hook is a variable defined in `simple.el'.
    Its value is (visual-line-mode-set-explicitly)

    This variable may be risky if used as a file-local variable.

    Documentation:
    Hook run after entering or leaving `visual-line-mode'.
    No problems result if this variable is not bound.
    `add-hook' automatically binds it.  (This is true for all hook
    variables.)