Very slim to none. A rogue planet would be very cold and totally lifeless, meaning it would emit very feebly indeed in the radio wavelengths. Spotting such bodies is very hard indeed (witness all the trouble they had finding Pluto and that's only at the (relatively) close distance of 39-40 AU.
"I could be bounded in a nutshell and count myself a king of infinite space, were it not that I have bad dreams" - Hamlet"Bones' remedies for problems seems to revolve around giving his patients a prescription of heavy drugs, booze, or taking them to strip clubs. He is either insane, a drug addict, or the best damn Doctor in Starfleet!"
- SFDebrisSDN World 6: The Kingdom of Orion