It's hard to tell if dad 'needs' son or son 'needs' dad. Try to ascertain what SPL etc, thinks of son and son's interaction with other scouts, confirming all appears balanced. See if scout his doing his fair share, participating on team building exercises. A bias of involvement from this direction could coax the appropriate separation of son and dad.
" there is no way the scout would advance in rank if not for dad's involvement" (scoutndad)- the young leaders could fix this, but most moms and dads help with the homework.