@donc Thank you for that - yes I am unduly pessimistic. Put it down to age ! Over here at the moment, anyone over 70 is almost expected to succumb to coronavirus if they catch it, and we know we will be the last to receive any protective vaccine. There has been a drive to get old people to sign DNR (do not resuscitate) notices. Which I consider an obscenity and would refuse to do.
Also - I admit I have never experienced a dog park. I guess they are a good second best if there is no wide open (or forested) space available and the only alternative is pavements.
My own whistle is the recall I have used on every dog through the years. To break up a ruckus I scream. They stop, turn around and ask each other 'what's got in to HER ?' But any fracas is invariably between members of my own pack, I don't have to break anything up with strangers because the ones we meet are off-lead 99% of the time and quite happy to meet, sniff and go their separate ways. If they weren't, mine would never be allowed off-leash.