What photographer hasn't been out with their clients and had tourists, park go-ers, children, dogs, etc. behind their subjects? We all have! It's nothing new that some people simply don't want to change their plans, just because we want to take portraits.
Well, that's okay! And I personally am not in the business of asking them to - if they don't notice, or don't want to based on seeing me with a camera... I'll remove them in post production.
Here's an example of that... Have no fear, Magic Wand Mouse is here! :-p