You need to get the dolmus to Marmaris to the main bus stop, there are regular buses running from there to Datca. We went to Datca last October, it takes about an hour on the bus and there is some lovely scenery and breathtaking drops on the way.
what day is you trip,we like going on saturdays,a group of us hire a mini bus so that does no tie us to times to come back and we can stop where we like to look at those fantastic views and those windmills.But we are a little earlier than our gang so might look at ICR trip.