I see reasoning with a toddler rather like my carefully explaining to the cat that her paws carry germs and for that reason, she isn't allowed to jump onto the countertop in pursuit of the butter dish or to attempt to smash her way through the closed kitchen window with her head in pursuit of the woodpigeon that is on the garden wall. Neither understand the minutiae of what I'm saying and, frankly, even if they did, neither would give two shits at that moment. But both understand a firm NO, even if they don't like it.
It's not a negotiation. It's an instruction.
Of course, with hats, it's illegal to superglue the things to their heads (cats or children), but if the alternative is sunburn and heatstroke, it's hat, stay under the parasol or home.
If it's not getting back in the buggy/cat basket, well, you get picked up and your raging little starfished body is put into the offending transportation device and securely fastened in to prevent escape.
If it's sticking fingers into a plug socket or chewing a power cable, you don't reason, you say NO and remove them from danger. As you do when they've got hold of a bottle of kitchen cleaner or an extremely pissed off looking squirrel.
If it's drinking your caffeine and sugar filled fizzy drink/mixer for vodka or nicking your chicken off your plate (or eating plastic), the answer is NO. It's not yours and/or the results will not be pleasant.
In terms of hurling herself on the floor, reins are great, as you can pick them up and carry a red faced, angry handbag to safety (as the throwing down will invariably happen when crossing a road) before putting them in their wheeled prison.
You're not there to please her. You're there to keep her alive, uninjured wherever possible and hopefully, to teach her that what Mummy, Nanny or Daddy says is what she has to do. Because her life may literally depend upon it at some point.
I don't negotiate with the cat. I don't negotiate with infants, either. Once her comprehension skills exceed that of the average domestic tabby, the human child can have further explanations. But at 18 months old, they've got a long way to go before they reach that point.