...
my $guard = My::Guard->new(sub { $sth->finish });
...
##</code><code>##

...
my $guard1 = My::Guard->new(sub { $sth->finish });
... some code which needs the protection of guard1 ...
my $guard2 = My::Guard->new(sub { .. clear up something else ..; $guard1; });
... some code which needs the protection of both guards, and the order of resource clearing is important ...