Preferably a dedicated dog poo bin, failing that a normal litter bin or if neither of those available, take it home with you and dispose of it with your own rubbish.
I saw a couple this morning walking their dog and it had a cone round its head but it also had the waste bag in its mouth. They stopped, took the bag away from the dog and chucked it against someones perimeter wall. Nice!!! :o//
They removed dedicated waste bins from my park a few years ago. Only normal bins now...at the entrances, and several scattered around the park. If I'm not near a bin, I take it home and put in our buildings bins.
With all the fuss around plastic these days, it's odd that nobody comments on this massive use of it. When I was a boy, you let your dog carp wherever - and some still do nowadays! Disgusting, maybe, but look at the plastic it would save ...