Advise on a possible legal matter involving hydro and dogs

[Seth81]

It doesn't matter if there is a contract or an agreement in place or not. This sounds like it would fall under an area of law called tort law. You need to prove three things.

1) The contractor owed you a duty of care. Which I think they did as they are working on your property regardless of anything else.
2) The contractor was negligent. I am not too sure about this one.
3) Measurable damages were incurred due to the contractor negligence.

I'm not a lawyer, but have had to study some law. But you can get free legal advice generally.

Also I am really sorry to hear about your dog, I would be furious.