difference between play/training walks?

[sydneyandratchet]

I would like to do more training with my dog while on walks, but the purpose of a walk is to give your dog excercise and in our case, so she can relieve herself. I want her to be able to sniff around and check things outs, but I want her to do it kind of when I say it is ok...how do I let her know when we are on a training walk, and when we are on a play walk, without confusing her?