Anyone else tried Bike Joring?

[Legs]

Definitely getting into Darwin Award territory here.

 

[Pat "5mph"]

Parks are there to be used.

Indeed they are.
Of course I don't know about your local park, but mine is full of elderly folks out for their daily stroll (zimmers and all), mums with prams and toddlers, small kids on bike and on scooters.
You'd scare the bejeesus out of other users!
I understand that you would do the bike joring at night, because you don't want to encounter people.
Is the park lit?
I tried once to cycle through an unlit park at night (sans dog, but with good bike lights), I was "attacked" by a myriad of yapping dogs.
Dog walkers (people) are out there even when it's dark.

In this instance, the risks outweigh the rewards for me, especially if its something that mentally stimulates my dog and helps him burn off the energy a working breed has.

Yes, for you it's fine.
For a third party in a collision with you, probably not.
On the by, I feel for the poor dog.
A dog from a working breed, imo, should not harnessed to a bike for the owner's thrills, it should be able to run in open land to burn energy off.