Our favourite place is Magalies Sleepy River, we've been there for day trips and camping, but it's an hours drive away and I need somewhere local for daily walks.
I love taking Bob to Irene to Jan Smuts House which is a 5 minute drive from our house. Entrance is R5 to park, there are toilets and lovely tea gardens. There is also a museum that charges R10 for entrance, but you can't take your dog in there and the 2nd and 4th Saturday of the month there is a market (dogs welcome)
You have to remember and you are warned about the dangers of walking on your own and there have been a few incidents in the past, but there have also been incidents inside the security estate that we live in.
I'd love to hear from you if you know of other local places where a dog can run off the lead in safety.