I use a flexi leash (the cord one, haven't found the tape one here), I love it when I'm in areas that he can run a little but though I don't trust him loose at.
I use the kind that takes 15 or 20 kilo's, though I just have 3 and 6 kilo dogs.... I have used the kind that takes about 10 kilos and I didn't trust it, I was so scared it would break one day.
I have the dogs besides me where there are cars near and if I see other people, dogs, cats etc. (then I stuck the leash so the dog can't go longer from me than 1 m.).
It's important to know how to use it