We demonstrate a method to create potential barriers with polarized light beams for polaritons in semiconductor microcavities. The form of the barriers is engineered via the real space shape of a focalized beam on the sample. Their height can be determined by the visibility of the scattering waves generated in a polariton fluid interacting with them. This technique opens up the way to the creation of dynamical potentials and defects of any shape in semiconductor microcavities.