We present two new designs of optoacoustic waveguides supporting nonlinear Brillouin scattering (SBS). The first design, optimized for forward SBS, comprises a rectangular core supporting a low-loss optical mode, suspended in air by a series of transverse ribs. The ribs are engineered to exhibit a complete acoustic stopband and suppress the transverse leakage of acoustic waves. The second design we discuss here is a realization of an Anti-Resonant Reflecting Acoustic Waveguide, which are analogues of optical ARROWs. These waveguides, capable of co-localization and guiding of both the optical and GHz acoustic waves in simple, translationally invariant waveguides, are shown to support backwards SBS.