Smoothed particle hydrodynamics (SPH) has been increasing in popularity rapidly in recent years and is being used for an ever wider range of applications. Central to almost all of these application is the inclusion of accurate wall boundaries. We present here a discussion of boundaries in SPH, in particular, focusing on reflected ghost-particle boundaries. We show how one can include curved shapes as geometrical objects and more generally as parametric non-uniform rational B-spline (NURBS) curves. By properly considering the reflection operation, we derive a correction factor that demonstrably improves the accuracy of the SPH solution and present examples to confirm this. NURBS are standard for representing both 2D curves and 3D surfaces. We detail how they can be practically included in an SPH implementation, including how to calculate various required quantities and reflect particles in the NURBS object.