Yeah, big talk for a Scottish engineer flying fifty times the speed of light.
Pioneer's signal could be picked up on Earth from beyond Pluto, transmitting a signal of only a few watts at its source. I have no idea what the lower limit would be from Mars. Even a fraction of a watt of response might be enough if a big enough dish was "listening." Obviously, a directional Earth transmitter could, even at this distance, probably hit the Martian surface with a bigger signal than any existing orbiter.
Radar reflectors would probably not be much good if you were trying to pick up the reflection against the reflection of the ground itself.