  We consider brane world models with one extra dimension. In the bulk there is
in addition to gravity a three form gauge potential or equivalently a scalar
(by generalisation of electric magnetic duality). We find classical solutions
for which the 4d effective cosmological constant is adjusted by choice of
integration constants. No go theorems for such self-tuning mechanism are
circumvented by unorthodox Lagrangians for the three form respectively the
scalar. It is argued that the corresponding effective 4d theory always includes
tachyonic Kaluza-Klein excitations or ghosts. Known no go theorems are extended
to a general class of models with unorthodox Lagrangians.
