  Here I develop the simplest method in order to evaluate whether or not the
Vainshtein mechanism can operate for a given set of parameters in a given
solution. The method is based on the formulation of the mechanism in terms of
the St\"uckelberg functions given in Int.J.Mod.Phys. D24 (2015) 1550022 and
arXiv:1305.0475 [gr-qc]. In such a case, the Vainshtein scale appears as an
extremal condition of the dynamical metric. If we fix the graviton mass, we can
define the effective Vainshtein scale. Then for parameters where the Vainshtein
scale vanishes or becomes smaller than the gravitational radius, the mechanism
should be absent. At the other extreme, if the Vainshtein scale is finite or
infinite, then the mechanism can operate. For consistency, if we define the
Vainshtein scale as an invariant, then we should expect the effective graviton
mass to become very large when the Vainshtein mechanism operates. On the other
hand, if the mass scale tends to zero, then the extra-degrees of freedom are
free to propagate. For clarity, here I analyze the effective mass behavior for
the different type of modes.
