  We study a general scalar field Lagrangian coupled with matter and linear in
$\Box\phi$ (also called KGB model). Within this class of models, we find the
most general form of the Lagrangian that allows for cosmological scaling
solutions, i.e. solutions where the ratio of matter to field density and the
equation of state remain constant. Scaling solutions of this kind may help
solving the coincidence problem since in this case the presently observed ratio
of matter to dark energy does not depend on initial conditions, but rather on
the theoretical parameters. Extending previous results we find that it is
impossible to join in a single solution a matter era and the scaling attractor.
This is an additional step towards finding the most general scaling Lagrangian
within the Horndeski class, i.e. general scalar-tensor models with second order
equations of motion.
