There is a bus that goes from the bus station in Marmaris but it will take about 4 hours to Fethiye and then a bus to Hisaronu.
It may be easier to hire a car for a couple of days.
Be careful if you decide to go by bus as there is a Hisaronu on the other side of the peninsular from Marmais about 30 minutes away.

It would be more practical to stay the night there, its a bit too far to do by public transport as a day trip. However as Jaytrip suggests hiring a car might be a better option. The other possibility may be going there at the beginning or end of your holiday, as it is in the opposite direction from Dalaman airport as Icmeler.