Our favourites are parks in the inner west. The ones in glebe are great. Its a scenic walk, poo bins & bags provided. The path is next to the water, but it doesn't have a high enough barrier to separate the footpath and the approx 1m drop to the harbour alongside. so not recommended for young/curious unleashed dogs or those who like to swim. Grassed areas too along the way.
sydney park is good, big enough that though there may be lots of dogs within the park, they are all fairly well spread out, provided you chose your spot wisely.
I would suggest you go to your council webpage which should have a bit of information on the off-leash parks in your immediate area.
This site has lots listed.
http://www.cityofsydney.nsw.gov.au/Residen...fLeashAreas.asp
Ones to avoid though IMO are certain areas of Centennial park and Bayview esp. on weekends and public holidays. Too many uncontrolled doggies and owners that don't pick up droppings.
Beaches in wollongong and south coast are great
HTH