  We develop a new technique for finding black hole solutions in modified
gravity that have "stealth" hair, i.e., hair whose only gravitational effect is
to tune the cosmological constant. We consider scalar-tensor theories in which
gravitational waves propagate at the speed of light, and show that Einstein
metrics can be painted with stealth hair provided there exists a family of
geodesics always normal to spacelike surfaces. We also present a novel
scalar-dressed rotating black hole that has finite scalar field at both the
black hole and cosmological event horizons.
