my $sth = $dbu->execute( \$dbh, \$query, \$errmsg );

My::DBU::execute is looking for one parameter (beyond $self), a scalar, $query. $dbh is being pulled from $self, so you don't need to pass it in. And I'm not sure what passing $errmsg into the method is supposed to do.

This would probably work:

my $sth = $dbu->execute( $query );

Note that returning the statement handle is kind of odd since you retrieve the $rows inside the method.