I know of 3 unmarked strips within the Melbourne Basin, that have no overlying CTAF and their location puts them on 135.7...there are probably more.
These 3 cannot recieve ATC on the ground.
So it is unlikely ATC will hear them, and 135.7 is FIA SFC - base of CTA.
So what is the problem with those aircraft when taxying making a broadcast on 135.7 like:
"ALL STATIONS, ABC C172 TAXYING AT PRIVATE STRIP 10NM EAST OF WHITTLESEA; ON DEPARTURE TRACKING TO THE NORTH BELOW 5000 OCTA".
- that's them using the most appropriate frequency per AIP;
- other aircraft on 135.7 transiting the area will hear the broadcast, and will if necessary take avoiding action or make two-way contact and arrange same;
- if the level of traffic and associated chatter at this or the other strips develops into a problem, one of the measures previously outlined will be taken.