sub meth1 { obsoleted }
sub meth2 { obsoleted }
sub meth3 {}             # do nothing, quietly.
# [...]

sub obsoleted {
    require Carp;
    Carp::croak "obsoleted method called"; # exception, with stack trace

    # or, just complain but go on with the show.
    Carp::cluck "obsoleted method called";
}