Good advice here.
My comment would be to spend a LOT of time training the dog to run to heel on command., This is crucial, especially with regards to traffic, other runners and, most importantly, livestock. With my dogs, I would spend a lot of time running them at heel on a lead through livestock, then introduce slow walks until any desire to 'go off' was completely controlled. Only then would I introduce off lead running, initially at some distance away. My first (and best) dog got this completely and would run so tight to me that, at a distance, there was no way you could tell she was off lead.
That being said, the lead was used whenever an expected interface with animals occurred. The training gave me confidence that I could control her if we unexpectedly came across livestock or were on open fell with loose animals.
Still miss that Jen!