Irresponsible dog owners ( includes swearing)

I treated dog and place for fleas yesterday, as maintenance, as always, WE WERE CLEAR OF FLEAS. THIS WAS MAINTENANCE

My Dog played with and said hello to a dog earlier when out, 

I HAVE Now found live ones AGAIN.

HOW THE FUCK can i rid of them (or prevent them) when others dont give a fucking shit. VERY ANNOYED.

We were clear of them for last couple of months. But if others DONT GIVE A SHIT then WTF do i do?

REALLY FUCKING PISSED OFF NOW.